● iStar Optical’s Phantom FCL 140-6.5
tested and written by Josef Ladra, Sep-24, 2021
I have no financial or other interest in iStar Optical, its owner and employees. All tests were performed and described to my best abilities of a highly experienced amateur astronomer.
iStar Optical has been successfully manufacturing 127-250mm F5-F15 achromatic lenses for many years. These lenses are also purchased by various professional manufacturers of achromatic telescopes, as well as by amateurs who build refractors for themselves.
Technologically advanced achromats with the designations R30-T, R35-S, and R50-S (Anastigmatic, T-thick, S-slim) are also very well known because the optical design reduces chromatic aberration by 30-50% when compared to Fraunhofer’s conventional achromat designs. This is due to an improved false color correction due to incorporation of a dense flint (type of an ED glass) in the design.
H-Alpha (solar) 150mm, 228mm, and 250mm lenses, which are used by solar observers and imagers achieve outstanding results, have also become very popular and successful on the global market.
Recently, iStar began to sell the long-awaited apochromatic telescope Phantom FCL 140-6.5 and has also designed a 170 / F7 model.
In the first series, the OTAs were manufactured with a standard tube length with matching 100mm (4”) rack and pinion focuser with 80mm tube travel. This is a fairly common issue where a standard length of the main tube sometimes does not allow the use of some accessories with a longer optical path. Most manufacturers end up producing their telescopes with shorter tubes and then customers are forced to purchase an extension tubes of various lengths to remedy the problem. iStar approached this issue from a different angle. Even though iStar is still producing a certain number of telescopes with standard tube lengths, the second and latest series is being designed and produced with a removable (threaded) 80 mm rear section of the tube. By removing the rear section it is now possible to use the scope with all types of bino-heads (binoviewers), filter wheels + OAG, other specialized imaging equipment requiring longer back focus distance. For example, my own Baader-Zeiss Mark V binoviewer still have a 25 mm reserve in focus.
As can be seen in the next picture, with the OTA not shortened (the 80mm rear section attached), the telescope is slightly longer than the TEC 140 / F7. However, after shortening the tube by removing the rear 80mm section, the Phantom is significantly more compact than the TEC 140. The Phantom focuser has 80mm tube travel and has a rotary lock mechanism attached via M61 thread. Unfortunately, on one of two tested Phantom FCL 140-6.5 OTAs, this mechanism does not clamp the accessories 100% and tends to slip slightly from time to time. The mechanism is secured with several worm screws and is attached on a M63 internal thread into which other accessories such as a flattener/reducer (F/R), cameras, etc. can be inserted.
This is an illustration of how you can disassemble the rear section of the focuser for the use with other accessories.
I decided to compare the Phantom CFL 140-6.5 with the top-of-the-line TEC 140/F7, which was produced in the ED version, using FLP-53 optical glass manufactured in Ohara, Japan. Today it is produced in the FL version (CaF2). The TEC 140 refractor has an aplanatic three-element oil lens, which means that the lens behaves like a compact optical element with two optical surfaces. This offers an advantage in contrast, as it creates a minimum of reflections over the air-spaced triplet used in the Phantom, which has six optical surfaces. However, when observed, I did not find a difference in contrast in the image of the Phantom and TEC refractors. When I first looked at the diffraction pattern of the star Vega, it was immediately clear that the Phantom has a better color correction of the spectrum than the TEC, which was an unexpected surprise to me. I compared the in/out of focus star diffraction rings and both telescopes showed textbook set of concentric rings.
The diffraction pattern (IN/OUT) on Arcturus shows the slightly turned-up edges of this particular telescope lens, however, it is completely within the limits of high surface accuracy of RMS 0.024 and the resulting excellent Strehl 0.977.
The Ronchi test shows the Phanotm has an excellent lens, and I have no reservations about that. The objective collimation was checked by the GMK collimator (Grzybowski) and shown to be practically perfect. The inside of the telescope tube is well blackened and there are no shiny reflective surfaces anywhere. The telescope has three knife-edge baffles mounted inside the tube.
The next was a photographic test, showing stars without chromatic aberration, and how big of a field of view can Phantom actually produce (the full resolution image must be opened in a new window). I took the first cropped image with an APS-C format using non-modified SONY A7SII (pixel size 8.4 μm). It can be seen that near the corners, the stars are beginning to have an elliptical shape and being slightly out of focus that is expected from a very fast APO triplet. However, the specially designed Starizona Apex ED-L reducer / corrector (R/C) designed for APS-C sensor, or WO flattener 68III for Full Frame, fully remedies this issue (Starizona is currently testing their brand new FF (Full Frame) field flattener matched to the Phantom FCL 140-6.5. These new units should become available for sale by early 2022). Other universal field flatteners/reducers can also be used. There is absolutely no chromatic aberration visible on white stars. Unfortunately, I took tests in the MSA 20.4 area, so I used a SkyTech QuadBand filter on some images, which turned out to be inappropriate because it creates a visible halo around the stars. There was also a considerable amount of moisture in the high layers of the atmosphere.
Following images were taken using ASI071MC camera (4.78 μm pixel) with and a QuadBand filter from SkyTech.
In the next series of tests I performed observing the sunspots, and here again the Phantom proved to be practically flawless. Image reproduction of the spots, granulation and foculae, all in great contrast, everything as it should be with a high-quality refractor.
Next, I observed Jupiter and Saturn, attaching Zeiss Mark V binoviewer without power-mate and Nagler 5 mm eyepieces. The image quality was excellent with great level of contrast. When observing stars, globular clusters and DSOs with the Panoptic 24 mm eyepiece, the stars retained perfect image quality all the way to the very edge of the field of view. Absolutely comparable image quality with my TEC 140.
From what I was able to see, I conclude that the optics belongs to a Super APO class, which is highly suitable for both visual observing and astrophotography. Unfortunately, I have to state that the TEC 140 lost in the direct side-by-side chromatic aberration comparison test, otherwise the TEC is practically perfect from the optical point of view. The Phantom FCL 140-6.5 is, therefore, a great all-round refractor, and the manufacturer has promised to remedy the minor mechanical issue with the amount of “grip” of the rotary lock. Therefore, iStar Optical can be congratulated on a very well made optical instrument.
Technical specification of the telescope:
Lens diameter: 146mm (class FPL-53 (Hoya FCD100) + 2 x ED glass) FMC layers on glass-air surfaces
Clear aperture: 140mm
Focal Length: 910mm (F/6.5)
Theoretical max. Resolution: 0.8 "
Focuser: 100mm (4.0 ”) with reductions to 2” and 1.25”, with rotary locking system
telescope length (retracted): 826 mm
Tube diameter: 144mm
Back Focus: 138 mm
Focuser tube travel: 80 mm
Dovetails: Losmandy 300 mm & Vixen 300mm (each scope is supplied with both) the Vixen dovetail serves as a handle
Fully Retractable dew shield with lock
Weight: 10.1 kg (including CNC machined tube rings and dual dovetails
Guaranteed minimum Strehl: 0.90
Guaranteed minimum PV: lambda 1/5
Manufacturer's website: Istar-Optical.com
● iStar 127 mm (5”) R30 F/12 Doublet Refractor Review
November 19, 2019, by Michael R. Nofi
My first telescope was a refractor. As a star struck 8-year-old it represented the ideal image of how a telescope should look. It was a model 9TE-5 Tasco 60 mm (2.4-inch) f/11.7 700 mm focal length alt-az telescope sold by Sears, Roebuck and Company. It was advertised disproportionally as a 234X telescope. With a refractor you could aim directly at the stars. In a Newtonian you look indirectly at the stars sideways. How a reflecting telescope works just didn’t make sense to my young mind. I have had several reflector telescopes over the last 60 years, but I always gravitate back to refractors.
I have always been a visual observer. The nights when the eye was the best detector for viewing critical details on lunar, solar, and planetary bodies changed in the mid-1990s ending a tradition of visual observing for scientific purposes that began 400 years ago. The advent of solid-state detector technology (e.g. CCD and CMOS) coupled with computer processing made it possible to exceed the amount of detail the eye could detect through “lucky imaging.” This new technology was quickly adopted by the amateur astronomer community.
Looking back, I was fortunate to have had 33 years of observing experience during a time when amateur astronomers could compete and occasionally exceed what professional astronomers could accomplish observing lunar and planetary objects. Still, to this day, I prefer to see photonic images of the many wonders of the universe directly on my retina. Is this silly? Perhaps.
Now is the best time to be an amateur astronomer, especially for refractor aficionados. Given the popularity of astronomical imaging, refractors are an excellent choice. They are perfect for grab-and-go astronomy and robust enough to be transportable. They are also affordable for most people. The main cost driver is the quality of the objective, which is dependent on the lens design, type of glass, and the care in fabricating the lens to a strict specification. The second most expensive item is usually the focuser.
Having observed with premier telescopes such as Stellarvue, APM, Astrophysics, TEC, William Optics, and Takahashi, the imaging quality of these exceptional products has set a new standard in refractor performance. Each manufacturer has a different design philosophy, but one thing they all have in common is these telescopes are smaller, lighter, easy to setup, store, and transport than their predecessors. Best of all, with the advent of the new ED and APO designs, the chromatic aberration that plagued refractors for over 400 years has been largely eliminated. Aperture for aperture, a high-end APO can exceed any other telescope design in terms of optical performance, irrespective of price. The future looks very bright for refractor telescopes.
Many of these premier telescopes come with a Strehl ratio optical certification. The Strehl ratio is defined as the central intensity in the aberrated pattern Airy disk over the central intensity in the unaberrated Airy disk. A Strehl of 1.0 is perfect. For reference, the Strehl of the ¼ Rayleigh’s limit Strehl is 0.80. There are many variables that define a good optic that one number cannot capture. Most observers can’t tell the difference in real world objects between a Strehl of 0.90 to 0.98. A star test will show the difference, but it takes a lot of patience to learn how to interpret star test patterns. Star testing can become an obsession. The test tends to be too sensitive and many fine optical systems do not meet the requirements of identical diffraction patterns on equal sides of focus. This is especially true of fast refractors (< f/7).
While the objective lens is the most important component, tube baffling, enhanced optical coatings, lens cell design, diagonal, and eyepieces are also critical.
Though suitable for visual observing, the new APO refractors are primarily designed and optimized for imaging. Fast refractors with shorter focal lengths (< 700 mm) do not make the best visual telescopes for lunar, planetary, and double star observing. To achieve a high magnification requires short focal length eyepieces with poor eye-relief. A Barlow can be inserted between the objective and the eyepiece as an image amplifier. These are built into many short focal length eyepieces, but all this extra glass and potential issues with collimation of stacked components can compromise image quality. Keep in mind that objective lens Strehl is not the same as total system Strehl. Many of the advantages of long focal length refractors are discussed in this review.
Cloudy Nights Classified
Several months ago, I saw an ad in Cloudy Nights for a used refractor. The scope was a 5-inch iStar f/12 doublet. I prefer the simplicity of doublet refractors because they achieve thermal equilibrium faster, they have superior image contrast, and a higher transmission factor than a triplet. Long focal length refractors are also less prone to errors in manufacturing tolerances (i.e., collimation, centration, wedge, and transmitted wavefront). In the future, the reduction in the cost of new optical glasses and aspherical generated lenses will simplify objective designs reducing them to no more than two elements making triplets unnecessary.
Several days passed and I could not stop thinking about the telescope. I showed pictures of it to my son for a second opinion. He asked me if this telescope is better than what I already had. My simple answer was not likely, since It would have more color. This was a “Eureka” moment. I realized that telescopes are like your children. You may have a favorite, but you love each one unconditionally, accepting their quirks, and flaws. Each telescope I own has a personality with characteristics are not easy to put your finger on. Some telescopes are immune to being judged for their optical performance alone. Sometimes it is not a question of one telescope design being better than another, but one of simply being different. For example, for observing Jupiter which is better—the view through a 6-inch f/8 Newtonian reflector, or a 6-inch f/8 achromat? All other things being equal.
I went on the Cloudy Nights refractor forum, to see what others thought of iStar Optics and telescopes. Reading through the threads there was a lot of interest and excitement about these new scopes. Questions about the company, the owner, where are the optics and tube assemblies made? Are the optics certified? Are these scopes any good? How do these scopes compare to the competition? Then someone had a bad experience with a telescope they ordered. It was most likely damaged in shipment. All second and third-hand information (nearly all one-sided) was shared on the forum. Speculation was rampant. Nasty emails followed and the owner of the company was literally roasted without any way to properly defend himself. This type of behavior continued for several weeks. For a new business, mostly dependent on the internet for communication and exposure to the marketplace for survival, this is a death blow. What a horrible thing to have happened. Worst, it severely damaged the company’s reputation. All started by one individual and then, unfortunately, others (like a hungry pack of hyenas) joined the cause.
What I know of the telescope business is this: No one goes into this business to make lots of money. The opportunity to get rich quick is just not there. People go into this business for the love of the hobby. The commercial telescope market thrives when there is competition. Where would Celestron be today without Meade (and vice versa)? Innovation occurs when we allow others with a different vision to bring new products to the market. As consumers we are all better off when there are more choices available to us. Competition also helps keep prices low.
The creation of every refractor telescope has an interesting story behind it (a story not often told). The design of a refractive optical system has many degrees of freedom, more so than any reflective optical design. This affords the optical engineer the freedom of choice when selecting lens design parameters, i.e., number of lens groups, number of lens elements, clear aperture, glass type (index and dispersion), radii of curvature, lens shape (e.g. spherical, aspherical, etc.), lens thickness, lens spacing and even the design of the optical coatings. The challenge is deciding how to work within and hopefully overcome many of the constraints dictated by the laws of physics and economics. Within these constraints, the lens designer designs a lens with performance properties of their choice. This makes each lens design unique, and to the lens designer personal. As a class of telescopes refractors have more character than any other telescope design.
The iStar telescope started as an idea in someone’s head. It was brought to market to provide a different astronomical experience to potential buyers. An experience that is manifested in optical performance. In a metaphorical sense it has a personality unlike any other design. The truth of the design resides in the star test and, most importantly, in the quality of the image seen through the eyepiece.
I am sure there were many obstacles for iStar along the way, as there is in any new business venture. And to think how much damage to one man’s dream can happen by one person trashing a company that he knows nothing about, merely by typing careless words on a keyboard. These are the same people that defend their actions as, “I was just expressing my opinion, which I may remind you I am entitled to!” They write an insult and then end it with LOL. If you take offense, they accuse you of not having a sense of humor.
I decided to go to the source and called iStar Optical to talk to the owner. He was friendly, and knowledgeable, and answered all my questions to my satisfaction. Like me, he loves refractors. After our conversation, I continued to search the internet for more information on iStar refractors. I asked myself, what differentiates these telescopes from others on the market? It appeared iStar’s strategy is to bring large aperture fast f/ratio refractors to the market primarily for use as deep sky (RFT) scopes. They also offer long focal length quality lenses, likely to compete with D&G. All the information on iStar was favorable, and while I did not find comparative reviews of these refractors, there were no negative reviews.
I preferred to buy a new telescope, but iStar no longer makes complete tube assemblies and I was not interested in purchasing an objective and building my own, so I purchased the used telescope posted on Cloudy Nights. The seller was a pleasure to work with, friendly, and knowledgeable. He gave me a good assessment of the performance of the telescope. It was everything the seller said it was and it arrived undamaged and in like-new condition.
It is huge and heavy, weighing in at about 27 lbs. with Parallax Instruments tube rings and steel Vixen style dove bar. I can still lift it though. The OTA is probably too large to be taking in and out of the house, so be careful with your sliding glass door!
The tube is fabricated out of 3 mm thick aluminum-magnesium alloy that you could mount under the wing of a fighter jet and launch missiles out of! No need to worry about denting it. It is powder coated with crinkled matte black paint, and, while black is not the best color for a telescope by day, it is a better color than white at night for two reasons. First, black helps to enhance and maintain night vision, and second, black paint has higher emissivity than white paint and will re-emit infrared heat faster than white. The matte finish also has more surface area than smooth paint which further enhances reradiation of heat. This is particularly important during cool down for nighttime observing.
The lens cell is massive, as is the dew shield, with the lens cell and glass alone weighing 6.6 lbs. The lens cell is easy to remove and features a push-pull hex bolt system for collimation. The lens diameter is 131 mm for a clear aperture of 127 mm, which is good because most lenses (from the final polishing process) have a small amount of edge turning. Having an oversized lens keeps this critical area of the lens outside of the clear aperture. In fact, it is possible to cheat when measuring the Strehl ratio by masking down the clear aperture ever so slightly (by several millimeters, or so).
This telescope is a new twist on a traditional achromat design. The lens was designed in the E.U. by Professor Zdenek Rehor and ground and polished in China. The tube assembly was designed, built and assembled by iStar owner Ales Patrick Krivanek in Arizona, USA. An equivalent European lens would likely cost twice as much.
The lens is described as a modified achromatic R30 (Anastigmatic) in iStar’s Rx lens series. It is hand figured to a monochromatic (yellow green) Strehl ratio of equal or greater than 0.93. By definition, an anastigmatic lens is corrected for spherical aberration, coma, and astigmatism. The minimum iStar surface quality for an optical figure is PV/4 which is ¼ wavelength (yellow green). The doublet is air spaced and uses crown glass and dense flint for color correction.
The lens design is optimized for the scotopic eye response (507 nm) which is biased toward the blue end of the visual spectrum. This gives the objective a minus red or cyan color balance and is an improvement over a standard achromat for both color correction and resolution. The difference becomes noticeable when viewing deep sky objects (especially open and globular clusters and planetary nebula). It should perform well on all the planets with some compromise in resolution in red objects, such as Mars.
The lens is optically pristine with no internal dust, sleeking, or underpolish. In the flashlight test at night I could not see a single sleek or dig on the surfaces of the lenses. Pitch polished glass has a certain “look” about it that is hard to describe. You often see it on Zeiss and Leica optics. The glass in this lens has that look.
Both lens elements are fully multicoated with a SiO2 based design. The specification states it is a broadband AR design. The optical coating is greenish-yellow in reflected color, uniform, blemish, and stain free. The stated focal length is 1476 mm with a clear aperture of 127 mm and an f/ratio is f/11.6, not f/12 as stated on the lens cell.
There may be some confusion about the meaning of the “R30” prescription rating for the objective. The R value is a measure of the improvement in color correction for a doublet objective relative to a standard achromat. Expressed in percent reduction in chromatic aberration, the R value limits are 0.0 (0%) for an achromat and 1.0 (100%) for a true APO.
The R value can be multiplied by the f# to get the equivalent f# in terms of a reduction in chromatic aberration (CA).
For a refractor, the amount of CA decreases by the lens diameter divided by the f/ratio.
Over 75 years ago, Sidgwick and Conrady each made a recommendation for setting a minimum CA ratio for an acceptable level of CA for achromatic refractors.
where f# is f/ratio or f-number and D is the objective diameter in inches.
The Sidgwick standard sets a minimum CA ratio of 3.0 versus the more stringent Conrady minimum standard of 5.0. As a point of reference my first 2.4-inch (60 mm) f/11.7 refractor had CA of 4.9 which is close to the Conrady standard and I do not recall seeing any signs of secondary color in this telescope. Applying the Sidgwick and Conrady standards to a 5-inch achromat specifies a minimum lens f/ratio of:
Sidgwick: f/15 and Conrady: f/25
If the iStar 5-inch f/11.6 system was a standard achromat the CA ratio would be:
This falls short of both CA standards and would require color filtration to achieve an acceptable level
Applying the R value as a factor in the chromatic aberration (CA) ratio calculation the chromatic aberration ratio for the iStar 5-inch R30 f/11.6 design becomes:
A CA ratio of 3.02 just exceeds the Sidgwick requirement, upgrading the performance of the scope to the category of an ED objective, but not to the level of a semi-APO.
According to Sidgwick, a 3.02 CA should have little or no chromatic aberration. Based on my visual observations it falls short of this expectation, but there is no question that the reduction in color is better than a standard 5-inch f/11.6 achromat. Calculating the % reduction in CA of the iStar compared to a standard achromat works out to be 30% (i.e., R30).
Let’s get back to the fun stuff. The rear tube ring and lens mounting ring are red gel coated polished aluminum. The candy red accent is attractive. Tube baffles (qty. 4) are the best I have seen in any telescope, regardless of price. They are screwed in place with flush mounted polished stainless-steel hex screws. The objective facing light baffles have a black foam annular ring adhesive mounted to the face of the black painted metal baffles to further absorb stray light. iStar pays attention to details.
The red anodized MoonLite 2-inch two-speed focuser is a perfect match for the telescope. I recently purchased an iStar 99.9% all dielectric 2-inch diagonal. The mirror is 10 mm thick BK7 with a 1/10 wave flatness rating. The measured FSM surface for scatter is less than a couple of my higher end 2-inch diagonals.
I first mounted the OTA on an Explore Scientific Twilight II alt-az mount with an extended pier with 22 lbs. of transverse counterweight. While this setup was workable, the OTA proved to be too much for the mount. Next I tried mounting it to an FTX ver. 1 alt-az mount which handled the load quite well, but the Berlebach UNI 14 Astro wood tripod was too small. Finally, I mounted it on my Celestron AVX GOTO equatorial mount and with proper counterweights it worked surprisingly well. When the tube is pointing east and west, the settling time at the eyepiece is about 3 seconds.
Chromatic aberration is noticeable on brighter stars (as a deep blue halo). I am particularly sensitive to it, but it is not noticeable on stars greater than 2.0 magnitude. The previous owner commented that the amount of chromatic aberration in the iStar was the same as his 5-inch f/15 D&G achromat refractor.
The iStar has slightly less secondary color than a 1990s vintage Meade 5-inch f/9.3 Semi-APO ED and significantly less color than a Vixen Neo-Achromat NA140 mm SS f/5.7. Even though the Vixen Petzval 4-element refractor is an improvement over a standard achromat, it still has too much color. This scope came out 20 years ago and surprisingly, it is still being sold today.
The first large aperture triplet I purchased was a Meade’s Series 5000 5-inch f/7.5 Triplet ED APO. While it has less color than the iStar it was more than I expected from a triplet, limiting telescope magnification to (150X) on the Moon. I paid nearly $2,000 for this scope back in 2009. The tube assembly is front heavy, and the objective takes 45 minutes to thermally equilibrate. Field curvature is excessive, and the stars are bloated beyond 2/3 of the field of view.
In summary, the amount of color in the iStar is acceptable. Compared to the other fine attributes of the telescope, this aberration is easy to overlook.
Double Stars: The 5-inch performs admirably on double stars and eats them for a late-night snack. On nights of good seeing I was able to routinely separate double stars at magnifications of (150X) to (300X) to the theoretical limit. It does very well when detecting faint secondary stars near their primary star. One of my favorite views is Tyl (Epsilon Draconis). This is a 3.8 magnitude yellow primary with a 6.9 magnitude pale blue secondary separated by 3.2 arc seconds. A gorgeous double worth checking out! The previous owner was able to resolve 52 Orionis which is separated by 1.1 arc seconds both components magnitude 6.2 and saw two perfect disks with black sky between them. The objective holds up under high magnification (350X), behaving more like a larger telescope. Double star color is only slightly biased due to secondary spectrum. Faint secondaries are as small of a pinpoint as the definition of pinpoint will allow!
Moon: Good image contrast with some residual blue secondary spectrum visible in the lunar shadows beginning at (100X) and increasing up to maximum magnification. Missing is the red secondary color component which gives the haze of light in the shadows a distinctly magenta (or purple) hue. Craters (i.e., Tycho, Clavius, and Copernicus) are sharp, showing good contrast at high magnification (150X). All surface features are in focus over most of the field of view, and, under good seeing, I was able to see small craterlets at the very limit of resolution. A genuinely nice lunar scope.
Planets: Jupiter and Saturn show a narrow blue halo. The contrast in the cloud bands and zones is excellent and not overly compromised by residual CA. The color of Saturn is more white than creamy yellow or butterscotch. In moments of good seeing, structure can be seen in Jupiter’s Great Red Spot. In terms of CA, the color balance is cooler, biased toward the blue. This reduces the warmer colors in the planets, in particular red, though there is still plenty of orange-brown in Jupiter’s bands! Mars will be a good object to evaluate the objectives correction to red light.
Deep Sky: The iStar excels on deep sky objects, which typically is not a strong application for refractors. The flat field, lack of coma and astigmatism make for wonderful views of star fields. Both bright and faint stars show beautiful diffraction disks. Under good seeing, it is easy to determine when best focus, is achieved, occurring when the last vestiges of axial transverse CA disappear. Most of the stars in M13 are resolved into the core, giving an icy-blue 3D effect.
This lens really shines on stellar objects. Herschel’s Garnet Star (Mu Cephei) is a ruddy gem of a star – a beautiful orange–red hard diffraction disk. At (37X) Mizar and Alcor are very prominent in the field of view, burning so bright it dazzles the eye. When you focus on an open cluster, the first thing you notice are the pinpoint star images. You never see stars like this in a SCT! In side-by-side views of extended sources, the 5-inch has better contrast than the 8-inch SCT even though the 5-inch only has about 60% of the light gathering power of the 8-inch SCT.
Star Testing: Intra and extra focal images viewed through a green filter are nearly identical. Star testing shows correction between a 1/6th and 1/8th wavelength (estimated based on prior experience with testing telescopes).
Ronchi Null Test: Nice straight bands, right to the very edge of the aperture. Smooth optical surfaces are seen just off of the null point.
Tip: Use the Ronchi test to determine when the objective reaches thermal equilibrium.
My Favorite Telescope?
Unequivocally, yes! Five inches of aperture is a good compromise between size, weight, light gather power, focal length, resolution, and the ability to utilize 1 arc second of resolving power on nights of good seeing. On most nights, I can see beautiful, hard, eye-popping Airy disks.
The doublet lens takes less than 20 minutes to reach thermal equilibrium. The lens is not so thick to absorb and scatter too much light. At f/11.6 the objective has a flat field (similar to the Vixen NA140 mm Petzval design). Coupled with a 56 mm 2-inch Plossl eyepiece the iStar gives (26X) turning the scope into an RFT with a 2-degree FOV and an exit pupil of just under 5 mm (perfect for a person my age).
The slow f# has a generous depth of focus:
is the amount of defocus that falls within a ± λ/4 wavefront error making it easy to achieve and maintain a sharp focus.
Is climate change affecting the good astronomical seeing that I recall from years past? Over the last 15 years the seeing is so bad at my location that I considered taking a break from observational astronomy. On nights of bad seeing, where the object is fluttering in and out of focus, the greater depth of focus allows the image to stay in focus longer. With short focal length refractors, you have to chase the focus to keep a sharp image and if the telescope mount is shaky, good luck focusing on a bouncing image! Unlike slow optical systems (> f/8), fast optics require a two-speed focuser for fine focus adjustment. Another advantage of slow optics is they demand less correction from the eyepiece.
The number of nights of good seeing have more than doubled. The objective lens is 7 feet above the ground which improves local seeing and isolates the observer’s warm body away from the entrance aperture. Options for improving astronomical seeing are limited, so how much is an improvement of (1/5) to (2/5) on the Antoniadi scale worth?
Over the last month I have been observing the double star Izar in Bootes and have not had one night where I was not able to easily resolve the secondary with plenty of dark space between the components. None of these nights fell below (3/5) on the Antoniadi scale. Observing under similar conditions with a short focal length APO refractor, I rarely saw an Airy disk during poor seeing.
Using a more traditional refractor with roots in the past creates a bit of nostalgia. What little chromatic aberration remains adds to the overall experience. I am looking at the same objects that other amateurs have viewed over the last 400 years. As mentioned earlier, sometimes it is not a question of which is better, but more about being different.
The optical quality of the visual images seen through this telescope are nearly equal to my best APO. You can see differences in side-by-side comparison (notably color and contrast), but the differences are subtle. An APO has the edge in terms of “truth in image fidelity.”
Making side-by-side comparisons by alternating between telescopes takes a lot of time (with changes in seeing and trying to match magnifications using the same eyepiece). If you spend the time you will likely be able to glean a bit more information out of the superior telescope, but if differences are not quickly obvious it may be time to move on, accept the telescope as is, and use it to enjoy the views of the night sky.
One should consider the other features the iStar offers, e.g. flat field, long f/ratio, depth of focus, faster cool down, location of objective away from heat sources, use of simple eyepieces, and relaxed optomechanical tolerances. Speaking of optical tolerances, it is not well known that refractors are more forgiving of errors in optical figure than reflectors. The wavefront error (ε) of a refractive optical surface is given by:
where δ is depth or height of defect
and n is the refractive index of the glass.
A mirror by comparison is ε = 2δ. All these positive attributes enhance the observing experience, and I would not trade them for an increase in a Strehl of 0.90 to 0.98.
Another reason I enjoy this telescope so much has to do with outreach astronomy. Kids love big telescopes and no telescope shouts “telescope!” better than a large refractor. I tell the kids that this is the telescope Darth Vader used to keep his eye on the rebels on the planet Alderaan. The telescope is big, dark, and ominous!
During special events, when I have my telescopes on parade, I ask my beautiful grandkids which telescope they like best and their unanimous response is, “the big black one, Grandpa!” Frankly, at this stage of my life, that is good enough for me.
● Asteria AT 127-12 R30 OTA
May 2013, tested by Neil English
iStar Asteria AT 127-12 R30 OTA tested by Neil English
Wednesday; May 15, 2013: Well it arrived safely, late this morning. Opening up the large box, I removed the packaging and took a long hard look at it. ” Now here’s a proper telescope!” I said to myself, with a broad grin on my face. The instrument was exceptionally well packaged, with dedicated tube rings and a dovetail plate. Nothing moved or could move during transit. The Moonlite focuser I had chosen was packaged separately and thanks to the excellent machining of the optical tube (details to come) , it took just a minute to have it ready for mounting. Here are a couple of photos of the Asteria 127mm f/12, without its super cool, lightweight dust cap.
The iStar Asteria 127mm f/12 on my alt-az mount.
The beautiful objective lens on the Asteria.
A quick check with the chesire eyepiece reveals well aligned optics. I also had a quick look at the high power images of the willow tree I use for daylight testing. Very sharp images at 254x and 304x, respectively. Small amount of CA seen around branches at these powers but more than acceptable!
This is an exciting telescope!
Tonight actually promises some clear skies, so much more to come.
May 16 00:15h
Just came in from doing some preliminary tests. Star testing on Vega shows some infocus colour – at high powers – but to the very modest extent that(for me at least) makes the images more beautiful! First and second magnitude stars show this. The first round of star testing took place after the instrument was left outside for three hours. The breezy conditions prevented any dew from forming anywhere on the tube. Stars focus sharply to nice round seeing disks. Contrast is lovely! And the rich colours of the stars really jump out at you. Examining the intra and extrafocal images reveals very pleasing similarity. The spherical correction is very impressive. I was able to confirm this by looking for the characteristic generosity of focus depth (as judged by examining the Lyrae Double Double) only seen in a well corrected optic. Were it merely diffraction limited, this magical property would be non-existent. So, as a rough guess, I’d estimate the figure to be a smooth 1/6th wave P-V. Examining the slightly defocused images of third magnitude stars at high powers (300x +) showed no astigmatism or signs of comatic flare. No green filter was used. The pattern was well defined without one, so it ought be even more impressive when tested at mid-visual wavelengths (550nm). That’s on my ‘to do’ list.
This is a large and imposing instrument, with the weight that comes with it. That said, I found the Asteria to be be adequately stable on my Skytee but with some notable adjustments. First, because the ‘scope is rather front heavy, owing to a large lens cell and dew shield, I elected to raise the tripod legs by about 10 inches or so for improved ease of use while pointing at higher altitudes. In addition, I added an extra 10 pound weight to the counterbalance system. That configuration worked very well even in the somewhat blustery conditions this evening. I’m also considering mounting it equatorially with my old Cooke tripod.
My student, Ross, enjoys the play of light on some emerging horsechestnut leaves at 300x.
The views served up in the evening sunlight were most impressive. One of my students, Ross, was gobsmacked by the images delivered by my 5mm orthoscpic giving 305x on the sprouting leaves of a horsechestnut tree, a few hundred yards distant. Later that night, dozens of stars were easily resolved in the Great Globular Cluster of Hercules and the Ring Nebula stood out razor sharp and stark against a near jet black sky(deepest twilight). The telescope, appears to be a most excellent splitter of double stars (as I expected). Izar was beautifully resolved (one of the most picturesque I’ve seen in a while), as was Delta and Mu Cygni. I deliberately left out Lamda Cygni from this first light vigil, as I will only attempt this system when it’s gained more altitude and the conditions are calmer. Herschel’s Garnet Star in Cepheus was a most lovely red colour. Clouded over by 00:30h.
Dismounted the instrument and carefully stored it away for the night.
All in all, I’m deeply impressed by the first light adventures with this telescope. I’m more sure than ever that these long focus refractors are the very best double telescopes we can ever invent.
As you’ll see, the quality of the workmanship that went into the instrument is equally impressive. Will post some high resolution photos of the entire instrument tomorrow.
It just needs a name now.
Tiberius……. or, more fully, Tiberius Sempronius Gracchus.
Tiberius Sempronius Gracchus.
Thursday, May 16, 2013
Took the telescope apart this morning to show you how well made it is compared to your mass-market bling.
The instrument is beautifully powder coated and professionally rivetted.
The professionally machined adaptor that allows one to mate a variety of focusers – including Moonlite, Feathertouch and iStar’s own brand – to the optical tube.
The high quality, dual-speed Moonlite focuser.
More evidence of high quality machining as well as showing that the tube is internally flocked – neat huh?
Check out the baffling on this baby – perfect!
Close up of the object glass. You won’t find sleaks or coating imperfections on this lens compared to your bog standard Synta.
Side view of cell showing lens spacers and internal flocking.
Nice engraving on the massive lens cell.
The lens cell is fully collimatable- like any high quality instrument ought to be.
I tried a variety of eyepieces last night; Kelners, orthoscopics, Plossls, Erfles, modified achromats and Huygenians all work wonderfully well with this refractor. Heck, you can even use warm eyepieces with zero degradation in the image LOL!!
’tis the unassuming nature of high f -ratio optics that delivers this kind of performance.
The workmanship gone into this instrument is right up there with those I’ve seen from APM.
Now, do you really think you can get this kind of service – swift delivery, high quality fit-and-finish and fine optics – from even the likes of D & G Optical?
Still a Happy Bunny.
Monday May 20, 2013
The hottest day of the year thus far. Temperatures reached a very respectable 20C by the late afternoon. A sign of things to come? Well, we’ll see!
In the late evening, I mounted Tiberius on the Skytee in the hope that I might obtain a clear or partially clear sky this evening. The weather forecast gave me some grounds for optimism.
Tiberius soaks up the late spring sunshine.
If conditions allow, I will be conducting further star testing of the instrument, together with answering a question that was raised by a poster to this blog. Can I verify the reduction in chromatic aberration by 30% over a regular achromatic doublet of the same specification?
I happen to own a choice Skylight 4″ f/15 achromat. As described in great detail elsewhere, it produces minimal secondary spectrum around bright objects. Both Tiberius and the Skylight f/15(me Alvin) both have the same focal length, give or take a few millimetres – that is 1500mm. If I were to stop down Tiberius from 5 inches to 4-inches using a simple aperture mask, I ought to be able to see a difference on bright stars like Vega or Deneb or some such. So out came me Alvin for a short test against the iStar refractor.
me Alvin: The 4″ f/15 Skylight refractor.
Tuesday, May 21 02:05
I left both ‘scopes out for about two hours before commencing some tests. Weird, Haar like cloud (low altitude) moved in from the west-southwest (it usually comes from the east), slowly clearing off for short spells. I did most of my testing after midnight, in a prolonged period of twilight (not in the least sense helped by a setting Gibbous moon) but clear skies. Conditions were quite turbulent, yet I was able to effortlessly split Alula Australis at 254x using my Baader orthoscopic. I was genuinely struck by the view of Delta Cygni, set as it was just a little higher than the roof of my house. Using the same eyepiece I was able to resolve and hold the tricky companion despite the obvious turbulence.
From there, I swung my telescope over to Izar, now culminating and hence optimally positioned for observation. Once again, at 254x, I aimed Tiberius at the orange giant but to my chagrin, it was very poorly resolved! One moment it was there but for several more it appeared to have almost completely merged with its primary! Eh?
Looking up, I noticed the telescope was pointing just above a tree. I dismounted the telescope and moved the mount to a position where the instrument would enjoy an unobstructed view of the system. Well, the view in the Asteria couldn’t have been more different; this delicious colour-contrast pair was stably held and easily resolved with this 5-inch glass. Do trees create turbulence? I thought about that before but laid it on the back burner for a while. More to do here I think.
I ended the vigil with a long, relaxed look at Epsilon 1&2 Lyrae at 254x. Briefly promoted to disability, I was visited by a truly jaw-dropping apparition! I hadn’t felt this happy about a ‘scope since Tonya’s lens arrived back in the post from Cambridge (she now has a shiny new focuser?!)
I am continually impressed with how well the Skytee mount is handling this large OTA. Although the dampening times have increased to about five seconds, it is still more than acceptable for my needs.
After that, I went to testing the lens in other ways.
Temperature 12C, 1017mB rising slowly. Not as tranquil as I had hoped. Scintillation still obvious in high altitude stars.
Using a light green filter fitted to a 6mm orthoscopic (250x), I repeated the star test on Vega. In focus, the star resolved down to a clean Airy disk with a faint first ring fragmenting and reforming stochastically in the seeing. No sign of zonal aberrations either. The intra and extra-focal Fraunhofer diffraction patterns were nearly identical. The brightness and smoothness of the outermost ring either side of focus is a telling indicator of spherical correction as well as lens smoothness. All I can say is that Tiberius produces deeply satisfying results. I concluded once again, even in these less than perfect conditions, after studying the clearly illustrated diagrams on page 182-3 of Suiter’s (first edition), that the figure on this optic was somewhere midway between ¼ wave and 1/8 wave P-V.
I had to wait until after midnight before I got a good chance to compare the stopped down Asteria with the full aperture Skylight f/15 in regard to their colour correction. The test eyepiece was my 9mm orthoscopic yielding 167 diameters. That’s high enough to see the extent of the deep red-violet secondary spectrum. Concentrating once again on Vega, I judged the contrast of both images to be neck and neck, that is to say – beautiful! Was there a difference perceived in colour correction? Yes indeed! Where the Skylight presented Vega with a faint purplish halo round the Vegan Airy disk, its colourful display becomes more pronounced during more turbulent moments. The Asteria image was subjectively creamier, with less obvious secondary spectrum. Comparing the images many times (by mounting and dismounting each instrument) I felt comfortable reaching the conclusion that the iStar object glass was better corrected at shorter wavelengths than the Skylight. I assume that this tweak in perceived colour correction can be achieved by bringing shorter visual wavelengths into tighter focus with the all-important green wavelengths at the expense of longer, red wavelengths. The tweaking was modest though, similar in fact to that adopted on the far more expensive APM 6” f/8 Super ED doublet ‘scope I reviewed earlier this year for Astronomy Now. All in all, I’m thrilled to bits with the colour correction of this remarkable iStar refractor.
21:30h: Fortune continues to smile my way. Tonight looks good for more observing. No more tests for now though. I just want to enjoy my telescope. When an instrument like this comes along, it makes me wonder why I bother hoarding so many other instruments when I really don’t need them anymore. It all seems very silly, that’s all. Several instruments will now be seeking new homes.
My experiences thus far with this telescope leave me in no doubt that it was professionally made. The person who designed the optics clearly understood what he/she was doing. How else would I get such a nice telescope? Yet, just a few weeks back, the most remarkable thread appeared on a popular telescope forum, where some of the key characters attempted to assassinate the good name of iStar. All the evidence suggests that the quality control from this company is very high; certainly the three iStar telescopes I have had direct experience of (two of which I reviewed well before the current hupla commenced) presented no serious problems of any kind. It is also particularly noteworthy that the indivdual who had the greatest gripe against the company purchased a relatively complex design, which, I’m sure you’re aware of, are inordinately more likely to fall out of alignment while in transit. And yet when Takahashi, Astro-Physics or TEC, or some other high-end telescope company produce the odd lemon – no one shouts for their heads!
Oh you hypocrites!
Still, despite getting a full refund, this prickly Canadian – disgracefully in my opinion – continued his vitreolic rant against the company. Amusingly, the same guy settled on a large, Chinese-made Esprit triplet apochromat????!!!!
Other folk, despite writing long threads on their positive experiences with iStar telescopes ( yes, they can be accessed on tinternet), couldn’t quite bring themselves to supporting the company in their hour of need.
Hang your head in shame you cowards!
Should I be bothered where the optics of my telescope are derived from? Not really, but it would be nice to know. I am reliably informed that iStar produce all their optics in China but to a very high standard of quality control. The optical tubes are made in Europe and the United States. Have you got a problem with that? Where do Televue get their optics? Where do they assemble their optical wares? And what about that shiny William Optics ‘scope of yours?
Thursday, May 23, 2013.
Tiberius on an old equatorial mount.
The first clear night receiving my large telescope, I sat out on the roof of a three
● The iStar Phoenix WFT 204 “Comet HUNTER"...
by James Edwards / Elk Grove CA
A New Dimension in a BIG Refractor!
If there are any here who remember my numerous articles, you will know that when it comes to astro gear and how it performs I know a good telescopes when I see one!
After owning 47 telescope types since 2001, ranging from SCT Meade’s and Celestron’s to many many Takahashi’s in both reflector and refractor types (Yes I am the Originator of the Mewlon 250S), I wanted to conclude my hobby on a high note, NO I am far from ending my pursuit of amateur astronomy but this last refractor is the end of the road for me, and after 26 years and a tons of evenings out viewing the sky it’s come down to one last refractor!
The iStar Phoenix WFT 204:
I looked at a number of incredible refractors before I elected to go with an 8” version. Often times I go back to the previous types I’ve owned, Meade Ed’s and Takahashi’s and many more I have had the privilege and honor to view though and enjoy. I also looked at many types currently being offered, but it still came down to what I A. wanted my last refractor to perform like B. Size does Matter and C. the overall performance and quality, which the iStar 204 more than exemplifies!
The day it arrived I was astounded by its size, having never seen an 8” refractor in real life, but also the crate in which it was shipped in, engineered perfectly for its weight and the travel distance to get here, all in one piece and ROCK Solid! As I unwrapped the crate and looked inside, immediately my heart was racing, “ man that is ONE BIG scope” and as I pulled it from the crating not only was I impressed by its workmanship but by its finish, Big Black Sleek and a total BRUTE, OH YEA LETS VIEW!
The paint scheme is awesome, black pebble finish like, durable with a superb coating along with its blue dew shield ring and bezel which is also at the focus end, the same sweet blue finish, what a combination, especially for my mounting platform, a Solid Black set UP! (Enter in Darth Vader music)
The Total Set UP:
The Phoenix 204 comes with excellent machined felt lined tube rings, perfectly matched with an ADM “D” series dovetail which fit perfectly on my Losmandy G11 Gemini II mount ( my 5th G11 ) I also use a 12” pier extension because of the 204’s length and naturally my 11 is fully GPS!
The Phoenix 204 comes with an ungraded Moonlight rotatable focuser, with a 10:1 micro focuser, a 1.25” reducer and each end piece comes with copper inserts to reduce wear and set screw marks. I have and always will be a Feathertouch Fan, but the Moonlight is no slouch, it is buttery smooth and solidly built, no complaints here!
Test Night One…Talk about CRUMMY SKIES!!
I had read the weather reports forcasting marginal conditions with a chance of rain, but never the less with a gap in the clouds, I was hell bent on taking the 204 out with crummy skies and all!
After the counter balance was set and everything was a go, it came down to only a few deep sky objects for us to look at. M31 and M32 were very good, not anything to get excited about but with 1 out of 5 transparency and a ton of moisture in the sky, both views were exceptional, the Phoenix was more than up to the task… We spent the remainder of the evening checking out M51 and again the double cluster in Cassiopeia, pin point stars between 180 and 300 power, the 204 performed flawlessly, what a BRUTE this scope is it was meant for bad skies or good, we were all very impressed!!!
Test Night Two…Clouds again but BUT well worth IT!!
Again we faced marginal skies (2 out of 5 transparency), but even with partial cloud cover the 204 performed flawlessly. My make shift dovetail for my Telrad was alright, but one thing I will need to address to get a better finder platform. Overall the Phoenix was a marvel, star clusters looked very tight (Caldwell 14, M 22, 25, 54 to name a few ) and very detailed not what some may think about a doublet refractor, but again it’s an 8” Brute so the lack of a third lens more than compensated with its aperture! We waited for Orion to show (3am), and took a last look for the evening, it’s was very good but again the moisture and clouds brought in the overall transparency marginal at best.
Night 3 – Finally a NIGHT to BEHOLD!!!
The clear sky clock was solid all day (Saturday October 5th.) showing 5 out of 5 transparency and super dark seeing after 11 pm. I packed up the truck and headed to one of our local viewing spots, Wilton CA (not too bad for the outer farm lands)
Once the sky was at its darkest, I was immediately swept to the few objects I had previously looked at, I wanted to see how the 204 performed with great sky conditions, I was utterly impressed, THIS Scope ROCKS!!
The list of objects the 204 I was most impressive with, were open clusters and galaxies, on a planetary scale the jury is still out, but Mars and Jupiter looked good (3.5 out of 5)
Moonlite 10:1 focuser with iStar 2” diagonal w/custom Telrad sight
(note: Televue 41mm Panoptic)
My seeing list:
M31 / 32 / M101 / M51/52 / Double cluster in Cassiopia
Triangulum galaxy M33 /M 81/82 / The Swan M17 / the Dumbbell M27
The Hercules Cluster (M 13/ Abell 2151) / NGC 404 - MIRACH'S GHOST
The Orion Nebula - M42 / Comets: Linear - Ison – Lovejoy
Sunday Oct. 6th @ 6:02 am, the International space station
flew right over head just as I snapped this photo…
what a way to end a night of Astronomy!!
Conclusion and overall rating:
My conclusion and rating is simple. I give the iStar Phoenix 204 a 5 out of 5 rating in its class (Achromatic) and overall a 5 out of 5 in performance, fit and finish and the cost!!! Yes it is a big scope, but my G11 handles it perfectly, as would an AP900 or Celestron CGEM, and well worth the time and effort it takes to own a refractor of this size. 1 thing that iStar needs to improve on is the front lens cap, yes the stock cap more than amply covers the front objective BUT it won’t stay on securely. I had Joe at Astro Zap make a custom fit aluminum end cap for me, I have to tell you Astro Zap Rocks, it fits over the dew shield perfectly just like a glove and well worth adding it to my 204 set up…False color is prevalent on brighter objects (planetary, moon and larger stars) but guess what? The notion that “fringing” or “false” color hinders or hampers what you see in a “doublet” is phony baloney nonsense, WHAT the 204 gives you is breath taking views that more than compensate for any color that shows… This scope is a beauty to aspire to, the stock aluminum rings are excellent as is the iStar 2” diagonal and all in all this is one scope that will more than give you a life time of viewing excitement and pleasure… Owning an 8” refractor brings a new dimension in owning a refracting telescope but I highly recommend it to astronomers looking to upgrade, you're going to LOVE this Beast!!
Type: Achromatic / Number of Elements: 2
Lens Diameter: 210mm / Clear Aperture: 204mm
Focal Length: 1200mm / F/ ration: 5.9
Lens Coating: Fully Multi-coated
OTA Weight: 24 lbs. / OTA length: w/dew shield 48 inches
Lens diameter: 210 mm / Clear aperture: 204 mm (8")
Focal length: 1200 mm / F stop: F/5.9
Lens elements: Fully Multi-Coated
● 150 F8 R35-S ATM OTA, Superb Quality
December 2013, by Steve M
It's been a couple months since I've bought my 150mm f8 R35 and I wanted to let you know that I couldn't be happier. About a week ago I took my first look at Jupiter through the scope and I have to say that I've NEVER, ever, had a better view. The image was sharp, bright, and full of contrast. I had the power up to 70x per inch and the image was still holding together real well. I also put the scope to work on double stars and it performed like a champ. Finally, I took a color photo of the Crab Nebula through the scope (on a rather hazy night) and that image revealed internal structures I've never seen before in other pictures.
To sum it all up, this is one great telescope. Thanks for working with me to make it happen!
● First Light Report of ATM OTA Equipped with 100mm F12 iStar Optical Achromatic
December 2013, by Stanislas Maximovich, France
The last events about your 100mm lens F12. I did the tube construction during last saturday with a simple chimney smoke steel pipe mat black painted both side, 130mm diameter. No internal baffles. I recuperate the 2 ends of the previous tube for the lens cell installing and for the crayford ring installing. Tube rings and 50mm finder too. Alignment was simple with a collimated laser beam. Remains the collimation of the lens on sky. The first light was impressive. I pointed Algenib of m2.0 magnitude and observed the diffraction patterns of the star, intra, extra focus, at focus. Intra-extra pattern looked like a semi apo figure of same image. At focus until 300x magnification, the blue halo, rather a violet halo was very discreet and confidential with a clear first diffraction ring slightly of miscollimation (to be retouched with a 1/10th turn screw at the cell). Surprisingly the figure at 300x was clear without blurring (the vixen 102 didn't go beyond 270x). This could mean high acurate optical surfaces level. Sky conditions were height of Algenib around 55°, seeing 3-4/5 Danjon scale, transparency 6/6, windy.
I had a look on Uranus with 240x, the disk was knife-edge limb, The south pole of the planet seemed clearer, but difficult to say firmly. I had views of Jupiter, being only 15° above the horizon. In spite of the elevation I noted seeing "holes" where seeing level reached on few seconds period 3-4/5. Without filtering with 133x magnification the disk color was whitish (as with apo like ED design), the limb was surrounded by a thin violet halo of narrow width, almost absent when at focus.
GRS was near the limb, it appears alone with a narrow gap from the tropical band. Color was without doubt deep orange color. Banding was very clear with so many festoons and nodes in EZ when seeing was at its best. Comparing these results with the TAL 100 and the Vixen 100, I would say the present 100mm is more performing, more acurate, more neutral for the overall coloring of the planet Jupiter. It reminds me the Unitron quality with less chromatic aberration.
About the quality levels, the TAL 100 is a L/4-5 (coloring yellowish), the Vixen L/5-6 (coloring yellowish) and the iStar probably >L/6 (coloring whitish). These are only numbers coming from comparisons (the TAL and the Vixen being measured).
I would like to complete the tests with more time on Jupiter, on stars (for a complete star test), on Venus to see what can be performed on clouding features in blue, green and red channels (The TAL performed), on Mars too same channels.
As a first conclusion in spite of the short period of this first light, this is promising, it seems, the lens doublet seems to be an accurate one with extra low CA amount. I asked a F10 doublet, I got a F12 one. I think we can leave the order as it is with regards to these results. I will do a report with the use of the OTA nextl with a certain period of observation on planets.
My best regards.
2013/12/19 stanislas maksymowicz < email@example.com >
● Test of IiStar Optical 150mm F15 achromatic refractor
by Bartolomeo Montrucchio, Italy
● Perseus AT 150-15 OTA
Report by member „Rutilus“ at www.cloudynights.com
Very short report on my istar 150mm f/15.
Last night I was observing a few double-stars and the scope was taking high magnification very well. The scope seems to have a real sweet spot at powers ranging from 250 - 350x.
epsilon Bootis - Good clear split at 112x. Best view was at 325x, but powers up to 500x were very good indeed. I used a 2.5mm eyepiece for 900x and was very surprised at just how good the Airy disk and Diffraction ring pattern was. While past it's best, the view was still usable.
gamma Virginis - easily split with no problems, as was the 1.6" wide Struve 1932 in CrB.
gamma CrB - a real tough one at 0.6 - 0.7". At 500x, no split was visible, but the star displayed an odd shape with a bump on one side.
The only DSO I observed was M13. The view was much better than that of my 4 inch f/13 Carton or that of my now gone Tak-TSA 102. Bigger aperture showing itself here, over the 4 inch scopes. The cluster appeared as a mottled misty patch with many individually resolved stars visible. The view was very nice indeed at 70 and 90x powers.
Star-Test - Needs more than one night of testing but this is an initial finding with a green filter used. Racking the draw tube inwards, a nice set of well defined rings, the very outer ring was brighter than that of the others.
Racking the draw tube outwards - A less well defined view, the rings were harder to see, and the outer ring was much fainter. The pattern was quite ragged.
My initial thoughts are that the lens shows some under-correction, but I want spend more time using the scope before coming to a conclusion.
Had another night with the f/15 on double stars. Out of interest I fitted the lens wth a 100mm aperture mask to see how it compared to a Tak TSA-102 and FS-102.
The views were simply wonderful, with the most delcate first diffraction ring. The scope was in cruise mode at powers from 300-500x. The views were every bit as good as the Tak scopes.
To finish off, I went back to full aperture and observed Eta CrB. At powers of 643 and 900x, two Airy disk visible with a tiny black line between them. Looking at orbit charts for this star, I think the separation is around 0.8-0.9" at the moment.
REACTION BY CN MEMBER “7331Peg”
"To finish off, I went back to full aperture and observed Eta CrB. At powers of 643 and 900x, two Airy disk visible with a tiny black line between them. Looking at orbit charts for this star, I think the separation is around 0.8-0.9" at the moment."
Pretty good shooting with that istar cannon, Rut! Eta CrB is even tighter than that.
I was just looking at it a couple of weeks ago, and when I pulled up the WDS Ephemerides, it listed the 2013 separation at 0.667" (!)
Here's a link to the WDS figures -- starting with the first column of numbers (175.5 0.623), the years are lined up from left to right as 2011, 2012, 2013, 2014, and 2015.
Eta is the first one at the top of the list (STF 1937AB). I show the Dawes' limit for a six inch lens at .76" -- very impressive!
● iStar Optical 150 F 5 Binocular ATM project
by Bill Faatz, Sky and Telescope, April 2013 issue
● iStar Optical 150mm F/8 R30 versus Meade
January 2013, by Victor, Canada
I can just say: Oh boy, oh boy it is amazing view that I saw couple of nights ago through my iStar 6" R30! Finally theYukon had a warmer weather, just about -4 Celsius. I took the scope outside well before dusk. A little ice-dew shattered on the tube and the 2" diagonal. but when it became dark, I was ready for observing my favorite Jupiter. I can tell that the planet's stripes were amazing in my 16mm Zeiss eyepiece (75x)! I was so excited about the view that I started to push the magnification quickly and gradually to 120x, then to 200x, then even to 300x!
Well, far better images than in my Meade. In other words, they are not even comparable on planets. I have actually never seen the Jupiter so crisp and detail in my Meade refractor compared to my new r30 anastigmatic lens! In addition, the sky was partially cloudy, so that the Jupiter got faint frequently because of the high atmosphere cirrus clouds passing by! Can you imagine what this scope can do in an actually excellent night? The same night I tried to put in my 5x powermate in the focuser then I slid my 25 mm orthoscopic eyepiece in it. The image of the planet did not fell apart, however the sky conditions limited my useful magnification to 250x.
I am very satisfied with this lens. In addition, using the scope in warmer temperature yielded way less colouring than in minus 40 degrees temperature. I did not see ANY false colour using the 16 mm eyepiece. When I pushed the magnification higher, I started to notice some faint violet colour around Jupiter but it was so insignificant and faint that it did not even bother me at all.
Read more here
● 127mm F/8 Achromatic Doublet OTA vs. a 127mm F/7.5 APO Triplet
January 2013, by Brian from Darwin, Australia
Good bit of to and fro here guys , All the tech talk is as Matt says is mostly above my head but I have owned a North Group 127mm f7.5 triplet up until mid 2012 and now have an iStar 127mm doublet f8 .
I think I have now used the iStar ( 2 months almost now , on every clear night ) to make a quick comparison between the NG triplet and iStar doublet .
Ok the NG definitely has better controlled CA , that’s to be expected ( over $2k , compared to $630 total cost of build ) so is the triplet 3.5 times better , not on your life it was very good but not 3.5 times better , more like 1/2 x better .
The moon ,
the iStar shows a faint color fringe , the NG none , but the views are identical apart from that .
same as the moon , but I feel the iStar shows more intricate detail in the bands and GRS .And the CA disappears for me very quickly once I start observing the planet .
nothing between them up to 250x when the NG pulls away slightly. Both max out at about 340x .
Identical in every way .
Deep sky , Double stars ,
As above .
No , I am more than happy with my 127mm iStar Doublet and don’t miss the NG triplet at all , and I had the pleasure of building my scope myself, total satisfaction .
Thanks Ales and Mike for a world class product .
I will do an in depth review with photos soon.
You cant compare oranges with apples without trying both first .
Read more here
● iStar Optical’s FORFAX LTT 140-12 APO Refractor
February 2012, report by Ryan W., USA
I posted a first light report a week or two ago, but I figured I would give an update. When the scope came the nighttime temps had been hovering around 10-15F, cooling from ~30F during the day. My first night out I had some cooling issues because of the huge amount of high density glass up front. I went out both last night and the night before, 2 nights ago for 2.5 hours and 1.5 hours last night. The temperature during the day was about 55F, warm for this time of year, luckily the temp in my garage stayed around45F so when I took the scope out at night there was almost no cooldown needed. The temperature hovered around 40F both nights while viewing.
My set up is as follows:
Scope: iStar optical 140mm F12 apo, FL=1680mm
Diagonal: iStar Dielectric 2"
Eyepieces: Denk 21s and Denk 14s
Nagler 3-6mm zoom and Panoptic 24mm in mono mode, yielding 280x-560x and 70x respectively.
Binoviewer: Denk II binoviewer with power x switch
I took the scope out earlier in the week to determine the magnification factors achieved with the Denk II power switch. I was forced to thread the OCS into the nose of the diagonal instead of the body, yielding rather high magnification factors. I have a WO quartz diagonal on order that will allow me to screw the OCS onto the diagonal body, reducing the magnification factors by 0.1-0.4x (it will bring the OCS 2" closer to the BV by doing this).
These mags are as follows:
(I know these seem high, but were checked twice)
21L = 128x
21M = 197x
21H = 300x
14L = 192x
14M = 295x
14H = 451x (too much ;-) )
I took the scope out around 8pm EST the first night, let it sit for 20-30 minutes to try to get rid of any cooling issues. The set up includes a red dot finder, and a Tak fs-60c as a super finder with a 24mm panoptic yielding a 4.6* TFOV and 15x.
Lets start with a picture of the set up? Everyone likes pictures! I also added a second 1' pier extension to the Losmandy HD Tripod.
Sorry for the poor quality pics, tough to get good ones at night.
Oh, my mount is a DM6 on Losmandy HD tripod.
Here we go:
I enjoy mostly Lunar and planetary observing. I have owned a pair of 30x100 binos, a Meade 6" Ar6, AT111 EDT, WO Zenithstar 66, AT72ed, Z12 dob. My main scope as of late had been my Tak fs-60c while waiting for the iStar to arrive.
I decided to start with Jupiter, it was very high in the sky. Seeing was so-so and transparency was good at moments, but due to very high intermittent clouds, variable. I put the D21s in on the low power setting and took my first look. The image was much better than the first night out, very steady and contrasty. Here is when things got a little fishy, I pushed the power switch to the middle setting and noticed a little color around the edge of jupiter...this was odd to me because the first night out I easily hit 400x on Jupiter especially looking for color and found not even a hint. It occurred to me that the Denk IIs might be the culprit (maybe a collimation issue). Before checking I took the power up to the high power setting (300x) sure enough, a little color. I switched the whole scope into mono mode to try to find the color problem.
I stuck the Nagler zoom into the diagonal on the 6mm setting, 280x. This was close enough for me for a direct comparison to the high power D21 setting of the bino. There was not even a hint of color in mono mode. I cranked the power up to 336x on the zoom, still no color. I concluded at this point that the color (albeit a small amount) was being induced by the Denk IIs, I think they need collimation.
I decided that the color with the binoviewers was a small enough amount to observe with. I moved back to the binoviewers.
I started again with the low power setting of the binoviewers with the D21s. Great detail, even at this low power. I could clearly see the two main equatorial belts defined as well as a few fainter belts and shading near the poles. I have never gotten the planetary directions down (north, south east west) so bear with me. I could glimpse darkening and bulges in the two main equatorial belts. I pushed the D21s to the middle setting, 197x. The image was still very pleasing, with even more detail. The darkening in the main belts began to resolve. One bulge became an ovalish shape, i believe in the southern eqt belt (i may have things backwards, I will figure it out). I pushed the power to the high setting, but the seeing wouldn't allow it. I went back down the the medium power and stuck with jupiter for another 30-45 minutes. There were moments of better seeing in which more detail came in and out of view. The moons surrounding jupiter looked distinctly different than the surrounding stars. Even at only 200x the moons looked tiny and disc like. I wanted to get a better look so I put in the D14s. The view of Jupiter was very nice at 192x in low, just like the D21s on Medium. I quickly went from 295x on medium and to 451x on high. The view was boiling and bubbling, but i pushed the scope over to Europa and Ganymede anyway. They were clearly discs, boiling discs, but discs non the less. I wish the seeing would have let me push the power more on Jupiter.
The moon was near it's high point for the night so I decided to point the scope over that way. I started with the D21s on low. I could just barely get the whole lunar disc in the FOV. The view was very steady and crisp. Just a side note: at this point I had been using the Tak fs-60c as a low power finder and really enjoy seeing the objects in context before moving to the iStar scope. I moved to medium power and decided to cruise the terminator. I was just picking objects on my moon map and pushing the scope their way. My favorite of the night was (i believe) Walter, which is a crater with two small, stacked craterlets that look vaguely like a tiny snow man. The view was steady here at 195x so I pushed the scope to 300x. Apparently the moon can handle a bunch of power, because the view held very well. I kept moving up and down the terminator and spent a while away from the terminator on mare serenitatis looking at the tiny craters strewn around the gray plain. The colors were great, bright bonish whites to the ash like gray of the plain. I had a lot of fun picking craters like Bessel and Linne on the plains in the low contrast areas (away from the terminator) on the map and then easily finding them. The seeing stayed good enough for 300x for another 30-45 minutes before it started boiling a bit. I just dropped down to 195x (medium with the D21s) and continued viewing.
Another side bar, I had heard of a book titled "xx most difficult lunar objects to find" or something like that. Does anyone know what I am talking about? If so, let me know what it is please.
I then decided to try a few deep sky, but at this point the high, thin clouds were becoming more consistent. I pushed the scope to the orion nebula and stayed on the low power setting. The nebula was framed very well at 128x and the four main stars of the tapezium were clear and steady pinpricks of light. I also took a look at the double cluster in perseus, which was pleasing, but due to the high power produced by the Denks, I could not frame them both at once. Still, very tiny pinpricks of light. At this point the high clouds and brightness of the moon began to wash out any DSOs quite a bit so I started to pack it in.
After the first night I decided that I will probably pick up a 48mm brandon eyepiece. I do not do too much deep sky observing, but really enjoy open clusters. The brandon in mono mode would yield a 4mm exit pupil, 35x and I believe a 1.4 degree fov. Sounds nice.
Well, That was the first (full) day and all I have time to write at the moment. I will get to more later.
Feel free to ask any questions!
I am going to try to finish my report on my second of the two days in a row. Tonight (2/1) I had a plan for my observing as opposed to the night before. I decided to focus on Jupiter to start because it was very high in the sky. Then spend a little time on the moon again and finish up looking at the orion nebula, double cluster and give the andromeda galaxy a try. For the Dsos I decided to go in mono mode to try for a wider TFOV.
A new note: I just received my WO quartz diagonal and measured the new magnification factors achieved by screwing the OCS directly into the body of the diagonal.
The new factors for low, medium and high are:
low = 1.45x
medium = 2.1x
high = 3.2x
I only got the diagonal yesterday, so the old factors were the ones used for the second night of observing.
I set the scope out to cool for 20-30 minutes. The temperatures tonight were very similar to the prior night, but there was easily less wind. I pushed the scope over to Jupiter and started again with the D21s on low, 128x. It was clear that the seeing was at least a little better than the previous night. Jupiter showed just a little bit more detail at this power than the night before so I pushed to the medium setting, 192x. The image was stable as the night before but I could make out a little more texture on the globe. I could just barely see some banding instead of just shading nearer to the poles. The night before I 300x, or the high setting just plain didn't work.
Tonight I decided to push it to 300x and stay there for at least 10-15 minutes. Before when I tried to view at high power I would just go to a given power, and if the view wavered at all I would drop back down. Since my last serious sessions I have read as many observing reports here on CN from some more experienced observers. I learned (I think) to be a little more patient at high powers and wait for the seeing to come to me. I would say I would have about 10-20 good seconds out of every minute, given, these were not in a row. In the moments of good seeing the bands seen at 195x became a little more defined. The image scale (to me at least) seemed huge, I had never used much more than 200x on my previous scopes. I think that the scope could have held rather steady at 230x-250x tonight, but I didn't have an eyepiece combo that would work. I took the power back down to low and decided to just enjoy the view for a few minutes. The scope just presents a pretty view of Jupiter, I can't wait to test it on the other planets!
I coasted over to the moon. Tonight I wanted to start with my lowest power setting. I wanted to try to fit the whole disc in the FOV, but was just barely unable to. This led me to the conclusion that I need another 24mm panoptic... ;-) The 2nd panoptic (now on the way) and the low power setting with the new diagonal will give me 0.67* fov and 100x, which will be great for full disc lunar, and some great DSOs, but I digress.
Back to it! I jumped straight to the high power setting on the D21s and got to cruising the terminator, looking for nothing in particular. I did this for about 15-20 minutes, the view remained very steady. Great, sharp contrasty views. I took my eyes away from the eyepieces and noticed (thanks to the light of the moon) some clouds rolling in on the western horizon.
I coasted over to the moon. Tonight I wanted to start with my lowest power setting. I wanted to try to fit the whole disc in the FOV, but was just barely unable to. This led me to the conclusion that I need another 24mm panoptic... ;-) The 2nd panoptic (now on the way) and the low power setting with the new diagonal will give me 0.67* fov and 100x, which will be great for full disc lunar, and some great DSOs, but I digress.
Back to it! I jumped straight to the high power setting on the D21s and got to cruising the terminator, looking for nothing in particular. I did this for about 15-20 minutes, the view remained very steady. Great, sharp contrasty views. I took my eyes away from the eyepieces and noticed (thanks to the light of the moon) some clouds rolling in on the western horizon.
I figured I probably had about 15-20 more good minutes so I quickly switched into mono mode with the 24 pan in the focuser. I moved over to Orion and stayed for 10 minutes. The trapezium was tight and the nebulosity extended further than I expected. I didn't push the power at all because my time was running out.
I moved over to the double cluster. Beautiful view, little tiny jewels in the sky. I couldn't quite fit all of both in the FOV, but could easily center one and see the middle of the other. I think this type of viewing is where the 48mm brandon would shine. I stayed on the double cluster for 5-10 minutes and began seeing clouds. No time for andromeda, and with the moon up I hadn't expected much anyway.
Next night out I am going to put the scope through it's paces on double stars. Any suggestions on that front would be much appreciated! What is a good test for a 140mm scope?
I hope you enjoyed it, i sure did!
● Making of ATM-style scope with iStar 150mm F/15 achromatic doublet
by Eden Orion, Israel
I've got the lens after a Skype conversation and payment. The lens was sent immediately and after less than two weeks it was at my post office.
Making the telescope was a great job, some obstacles, but not too much. Finally it was tome to set the exact place of the lens. I've checked it with a first quarter Moon. The first view was fantastic. Very sharp, nice shadows. Than after the lens was set in place and a collimation process was made, I've checked it again.
It was a Full Moon night and i did not hope to see a lot. but as I've pointed the scope to the moon my jaws dropped! NEVER in my life I was able to see so much details in a full Moon! I was so in shock than a month later I've took the picture enclosed. I was with one of my friends Mr. Adi Cohen which is one of the most professional photographers in the country and also a deep sky photographer. He was also amazed by the contrast and lack of false color that we got.
You might see some slight color on the edge of the Moon, we both not sure that this is chromatic aberration, since it is more yellow that all other colors.
Eden Orion, Israel
(Note from iStar Optical: yes, the slight yellowish halo is indeed the false color / chromatic aberration. It is indeed very low and practically insignificant especially when compared to other brands of scopes. We are proud to offer a very inexpensive Classic doublets with truly excellent resolution and extremely low level of chromatic aberration).
● iStar Optical 5" F8 Achromat
January 2012, by Dave Gibbons
PART I (8th January 2012)
iStar 5” refractor, an honest review.
Some of you may remember I purchased an iStar5” f8 Achomat objective last winter and spent a little while constructing a scope machining various bits and modifying a meade ar5 tube adding a moonlite focusser and the promise of a review to follow. Well here it is!
Firstly I am not an optical expert or a great one for technical analysis with strehl ratios and p-v wavefront figures, I have, however, owned several dozen scopes and been an avid visual observer for 40 years and I know where the iStar sits optically within the Jumble of extensive data catalogued in my head- I just have a bit of trouble finding which bit goes with which scope these days!
I won’t go into construction as I have posted on this already.This post is all about what the scope can give under the night sky. Suffice to say It is a really substantial bit of kit fully collimatable with a genuine 127mm of clear aperture.
I had hoped the scope would prove to be a versatile, quick cooling good all rounder. In particular I had built it with binoviewing in mind and had cut down the donor tube to allow enough in travel to accommodate the extended light path binoviewers require. As It turns out I have had to reduce the tube length by a further 50mm and now do not require an ocr or barlow when binoviewing. It also sits nicely on my cg5 mount.
I was fortunate to own a truly excellent Tal 125r achromat refractor and I have always said if the iStar objective could match that I would be very happy. I’ve also owned several Meade Ar5 refractors- indeed one these supplied the tube used in the build, it had a poor objective.Also owned half a dozen Synta 6” f8’s as well as Tal 100r and 100rs, so have a good idea what Chinese and Russian optics are all about.
First thing I will state is that on highest power lunar, planetary and double star observation it comes a close second to the Tal 125r. The Tal could be taken to over 100x per inch on doubles on the very best of nights the iStar is good for 75x but then gets a little soft round the edges. Star tests are good but it definitely loses the stellar tightness before the Tal did. It is on par with the best ar5 I owned which is pretty good as this had a longer focal length of f9.4. I must add that last observing session I thought I detected the objective is not in absolute perfect collimation ,something I will address , but I still believe it would come just behind the Tal.
At f8 false colour is of course present on brighter planets and the moons limb. It is in my mind a tad less than is evident on the synta 6” f8’s and one thing I have noticed is when you do crank the magnification up it does not become overwhelming and is not an issue , I must add I have always found it easy to ignore false colour in an achromat but appreciate that some people can’t stand it and will never see past it. Although I would not wish to look through an achromat shorter than f8 !
It is very similar to the Tal125r on CA but is a magnitude worse than the f10 Tal 100’s as you would expect. Most definitely colour correction is slightly better than the Synta f8’s. It’s a trade off though with the iStar giving wider fields than the f10 scopes.
Where I have been blown away by the iStar is in it’s use as a wide field sweeper. I recently purchased a 2” skywatcher 38mm panaview eyepiece and it is a match made in heaven. I know it’s not in the league of super high end eyepieces but with the unchallenging f8 focal length it gives very sharp widefield images across 90% fov.
The fov just covers Orions belt with Alnitak and Mintaka being on the absolute edges of the view this is really impressive, a little under 3 degrees. The views of open clusters and starfields the double cluster etc, are absolutely stunning .Ah the colours of the stars are almost too beautiful for words, this is something people often miss about achromats but once you are looking at less than 1st mag stars the colours on show are jewel like and very vivid. I thought I had seen it all but many hours are going to be spent using this scope looking at galactic clusters and star fields and picking out brighter deep sky targets.
It’s wide field performance has surprised me, in as much as it has taken me in a direction I didn’t expect having always thought of myself as more interested in targets such as double stars, lunar and planetary observation, I just didn’t realise just how magnificent discovering the bits in between can be!.
I am so impressed I’ve decided to buy a sky tee alt-az and stick with pure star hopping and visual observation. I realise now that although I thought I knew my way round the sky and I do , there is so much I just have not seen.
Finally Binoviewing with the iStar , what it was made for. Lunar viewing is a joy the amount of detail 2 eyes give is just stupendous. Looking at Plato 4 craterlets are evident and a hint of another. The contrast and texture of the lunar surface looks almost powder like I can see the dust! A wealth of detail is visible in Jupiter’s cloud system and the 4 inner moons show different colour and tiny perfect discs. It was worth putting the scope together for this alone.
Building the scope has been a really fantastic project, I even got to do most of the machining myself on tube and counter cell, a real labour of love that was. You will never see this in the for sales section as it is the only one in the world and it’s mine, make your own!
Here's a few more pics.
PART II (16th January 2012)
Collimation is now bang on! scope absolutely on par with my TAL 125R.
Showed 6 Trapezium stars with ease last night and shadow transit on Jupiter stunning in binoviewers. Error was with Moonlite focusser not sitting square on the tube. Happy camper!
● First impressions of the new Perseus AT 150-8
January 2012, by Doug Herren
Newbie here to this forum... thought anyone interested in these scopes would like to see one. Fantastic build quality, and excellent optics... I'd estimate at least 1/6th wave at the eyepiece comparing to other scopes I have that have 1/6th to 1/8th wave at the eyepiece. Takes a little time to get one, but well worth the wait!
It took about a week after the adapter came to install my Moonlite for the clouds to clear so I could finally get a chance to look at something more than telephone pole wires and insulators.
The scope really has amazing optics, no doubt about it. I've used scopes of various makes with wavefronts at the eyepiece from 1/6th wave to 1/8th wave, and this refractor's optics exhibit the same sharp, small diffraction rings as these instruments, so while the test report puts it a hair under 1/5th wave, it looks like it's only because of a spike on one small edge, the optics perform closer to 1/6th or 1/7th wave.
Can't say enough about the build quality of the scope. It really exceeds what I expected and the photos on your website do a pretty good job indicating what one should expect.
Thanks so much for such great service and all your help, the scope is really just fantastic!
● Becoming a refractor addict after 35 years of dealing with SCTs and other mirror based scopes
January 2012, bty Frank Theys, Belgium
This is the first time I post in this forum and would like to introduce myself (I have been following the CN refractor forum discussions closely though since a few years and have learned a lot doing so).
I am 47 years of age, live in Belgium and have been in astronomy since almost 35 years now. I have possessed numerous telescopes so I have acquired quite some observing time spent behind the eyepiece and especially (well, 90% of the time) dabbling in astrophotography (without getting really great pictures to show off). I have gone from the simple 114 mm reflector to a 150 mm reflector, then a C8 followed by a C9.25, a Vixen VMC260, a 300 mm reflector and finally a C14. This in combination with the necessary photographic equipment going from the 35 mm film SLR to a digital SLR and CCD cameras. During those 35 years there were also times that astronomy was more in the background, for the common and obvious reasons : study, work, family, house, etc... The last years it has come more to the foreground again. I had a lot of fun during those times but also a lot of frustrations especially trying to obtain pictures with long focus telescopes and CCD's. In fact, the last year or 2 I have become to find astrophotography less fun and more of a chore, certainly the processing afterwards.
Now you all wonder "What has this to do with refractors?", I am coming to that. For a long time I have considered refractors useful only as guiding telescopes and rarely viewed through them. That is, until I bought myself a Vixen 114mm SS ED-doublet which was at the time considered as one of the better good buys for astrophotography (I am talking about the pre-digital era). Although primarily used for photography I also occasionnaly used it for visual observations. I liked it but I wasn't overly impressed compared to the views in my bigger 'guns'. When the digital era started this telescope was no longer state of the art and he disappeared more or less in a cupboard, to be used once or twice a year.
Two years ago, during the summer holidays, all this changed! Following a few frustrating months with my equipment (focus and guiding problems) I decided that I wouldn't bring along all my equipment but just my little refractor equiped with a new Moonlite 2.5" focuser, mounted on a specially acquired Giro II Alt-az mount. I also brought along some other pieces of the during all those years acquired equipment : a quality 2" diagonal mirror, quality eyepieces (Pan 35, 24, 19, Nagler 9,...) and a UHC-S filter.
It was during the preparation for the first observing session that I realised that it was for the first time that I would be using my refractor with those quality accessories (before that I used it only with a off-the-shelf 1.25" prism diagonal and simple eyepieces), on a simple Alt-az mount and ... under a dark sky. Mmmm.... interesting. The following hours would be one of the biggest WOOW! moments in my life! For the first time I was able the observe the North America nebula in al its glory with the 4° field of perfect pinpoint stars in the 35 mm Pan and UHC-S filter, the Veil was unbelievable, just panning the overhead MilkyWay with the Giro mount was a treat with all the stars and dark nebulae visible. Also observed were M31, M33, the other usual showpiece objects and some lesser observed objects. I had a total of 3 observing nights under very good (for Belgium that is) dark conditions and it was the best fun I had had in astronomy since decades!
SOO, after this experience I began to be more interested in refractors and visual observing and I began to follow more closely the CN refractor forum and other places dedicated to refractors. One thing lead to the other and...
*** I have to admit that I have now become a REFRACTOR NUT ! *** All those funny tubes with reflecting surfaces and light bouncing in all directions that need frequent collimation are gone and are replaced with REAL telescopes!
I have now a 70 mm TS ED (similar to Stellarvue 72 mm), a 80 mm F11.3 Vixen, an older 90 mm F14.4 Vixen, a 102 mm F11 TS achro (similar to AT102), a 114 mm ED SS Vixen, 130 mm F7 ROBTICS triplet (similar to Astro-Professional, the new MEADE triplet,...) and a 150 mm F5.9 TS achro (similar to AT150). A 200 mm F6 istar telescope is on order !!
What's more : I USE those telescopes often and I do now most of the time visual observing and only occasionally widefield photography with the 70 mm ED and DSLR. I also started to (re)appreciate observing the moon and planets with all those telescopes and can have as much fun with the 80 mm Vixen achromat on a PORTA mount as with the 130 mm triplet on my equatorial ATLUX GOTO mount. My motto is now "KEEP IT SIMPLE, STUPID!" and in doing so I am having more fun than ever. After all life is complicated enough as it is.
In that context I have to admit something else, something worse and probably not so popular on this forum : this motto has lead me in becoming a *** ACHROMATIC REFRACTOR NUT ! ***
Yes, you will have noticed there are quite some achromats in my telescope list. I am foremost a deepsky observer and it is a fact that aperture IS important for that kind of observing, so since big APO glass is very expensive I got myself a achromatic 150 mm F5.9 telescope which gave me such good quality images under dark skies (maybe more about this in a later post) that I am convinced that you don't need an APO for satisfying deep-sky observing. Don't get me wrong, an APO may be a bit better than an achromat but a slightly larger aperture can neutralise that difference and you would still have a less heavy telescope and a lot of money left on your bank account! In fact I have done some observing with my triplet 130 mm and the 150 mm achro, both mounted in parallel on the GiroII mount and to my eyes the latter is the clear winner on deepsky, even under medium to higher magnifications (180x with 5 mm Nagler). It is no surprise then that I have now a 200 mm achro on order.
When I am at home, under a mediocre light-polluted sky, I limit my observations mostly to the moon and planets, double stars and sometimes, when I am really itching for it after a long time without dark sky, the brighter deep-sky objects. For that I use the 130 mm triplet for those longer observing sessions and the smaller telescopes for 'grab and go' observing of the moon. That is until recently because I had another one of those eye-opening moments again.
I won't go in too much detail but on two consecutive nights my 100 mm F11 achro beat the 130 mm APO by a large margin! This even after a 2 hour cooldown of the latter (from the unheated observatory). I attribute this to the fact that the APO couldn't cope with the descending temperatures after sunset where-as the achro had no problem what so ever with it. I also clearly noticed the effect of the larger focusing depth of the achro : even when the image was oscillating due to the seeing the sharpness mostly remained as opposed to the APO who even when under good temperature equilibrium shows more unsharpness during those oscillations. I am now a believer of the long focus achromatic refractor for moon and planetary observations, at least under my climate conditions with rarely long stable weather conditions (thank you Neil English for putting me on the right track with your great articles here on CN). I admit the CA bothers me but in the end I prefer a colourfull stable sharp image over a colourfree unstable and often unsharp image. And besides, I discovered a secret weapon against the CA : my Denkmeier II binoviewer! Yes, using this binoviewer the CA was spectacularly reduced, to the point that it didn't bother me anymore and the details visible were not that far from those in the APO used under better conditions. So I am now also lusting after a 5" long focus achromatic telescope. D & G ? Or istar ?
I think that after 35 years I have finally settled on the type of telescope that I really like for my observing habits and conditions : the short achromatic refractor for deep-sky observing and the long focus achromatic refractor for moon and planets! Not that I would mind the odd APO.
Frank Theys, self-professed refractor addict
● iStar Optical 150 F/5 Classic Achromatic Doublet in ATM style tube assembly
by John Jarosz
I'll resurrect this thread to further report on the objective performance.
I was out at my in-laws in Iowa over Christmas. It's a rural area with a good dark sky. Christmas night was spectacular, clear, no moon, 40 degrees. Keep in mind that I'm using the Baader semi-apo filter in front of the 2" diagonal. My view of M42 had the most nebulosity I have ever personally seen visually. I now see how Stephen O'Meara actually can see the stuff he sketches. I'll never be able to see like him but I get the idea after my session on Christmas. Pleiades and Hyades were excellent as well.
The istar objective has more contrast than my 6" F4 reflector. I'm a believer, but I couldn't tell under city skies, I had to get out to the country with a good clear transparent night.
So thumbs up all around for the iStar glass.
● Perseus AT 150-12
December 2011, by Sky at Night Magazine, United Kingdom
● Huge observatory class 250 mm clear aperture F/11 R30 Anastigmatic Doublet objective lens mounted in an ATM-Style OTA
First light report by Mike Carman
Well last night my istar 10" F/11 R30 stunned the sox off me. Bear in mind it has not been collimated as one person cannot do it alone properly. First light candidate....Altair. A bright pretty blue white star. At 110x with my 25mm plossls and binoviewers CA was not apparent. Only at about 180x did CA start to show. Unlike my 8" F/13.3 Brandt the istar exhibited a warmer hue closer to my lavender hued Jaegers. The Brandt has a deeper blue violet hue. I was afraid even with the R30 glass that this 10" was still going to show more color than the 8".
To my astonishment it actually shows very slightly less color if you can believe it!! I get no more color with a scope that normally would be physically over 30" longer in focal length. That's the real bonus for me. A normal 10" F/11 would be more colorfull than my old 8" that's for darn sure. Jupiter's moons all had tiny flares at the bottom because of the collimation issue. But man could I see detail much easier than with the Brandt. Much better contrast with more saturated colors in the belts. The seeing was soft to boot. The really big surprize that in urban skygow I could easily see the the star next to M57...I could only detect it with averted vision with the Brandt. Globular clusters M15 and M2 were text book perfect and easily resolved across their entirety.
Tonight Jupiter is a fuzz ball so not much is going to happen there. I should have the scope collimated in a few days. The diffraction pattern inside and outside focus has the same exact perfect rings that the 8" has. Only difference is there is a slight elongation in the pattern that is easier to see closer to focus. But collimation will take care of that. All in all I'm extremely pleased. Ales Krivanek has come thru with high marks on a large lens this time. All other lens reports up to this have been highly positive also. I can tell everyone that as an experienced refractor user if anyone can best Ales more power to 'em but I don't see where istar could be outdone in this category for the money. Again Ales and US rep Mike Harden...
My oh my is all I can say! Hot damn man! The minute I viewed Altair I knew full well what this lens was capable of so no further use of the lens was needed. ;D Just a little wry humor to get your goats. Anyway this larger aperture shorter FL lens is outdoing the Brandt 8" F/13.3 on CA. There are flares and spikes at the bottom of all stars and Jovian moons. This because it hasn't been collimated yet. With a laser we also still have to adjust the 10"x32" tube so that it is perfectly on the optical axis. But even so the lens is showing as much detail and more between seeing turbulances. What really took me by surprise was the ease at which I could look straight at the star close to M57.
With the Brandt I had to use averted vision in this urban sky. Ales you and Zdenek will have a tough time besting this. Maybe you boys just got lucky....but what do I care now. ;D ;D I was able to get a 10" F/14.3 into my existing space.....that's what I was after. I even got the tube length correct so my binoviewers had an inch of in travel left with 25mm plossls and no barlow for star filled low power dark contrast sweeping in urban Omaha skies. That alone is worth the price of admission. Therefore to say that I'm a satisfied customer is the understatement of the day. Thanks to Mike H. for double checking those "other" two. ;D
Well I just finished three hours of test observing tonight with the new istar lens. It was cold and windy but the atmosphere was calm and transparent. I used that Brandt 8" F/13.3 for over 30 years and would have put it up against anyone's scope in that aperture range and would have come in second to noone. Tonight however I confirmed two things and several obvious. First of the obvoius is it's a larger aperture. So right off we know to expect twice as bright of an image and second the airy discs should be smaller or tighter....and they were. Now on to the confirmation that this lens is indeed better corrected for CA. In the normal scheme of things if you were to say that CA would increase dramatically going from an 8" F/13.3 to a 10" F/11 you'd be right on the money....right? Not so fast some of you self proclaimed experts. It is so very obvious to me that the 10" R30 is actually controlling it more.
Before replacing the Brandt I carefully estimated the extent of the bluish purple halo around Jupiter to be slightly broader than the S. Equatorial belt but not nearly as well defined gradually diffusing outward. The istar lens shows a much tighter purplish lavender almost to the extent of the N. Equatorial belt and sharply defined. The Baader Semi-Apo filter gives me the same "look" thru this 10" F/11 that I see thru my Tasco 4-1/4" F/15. That to me makes me an extremely happy camper with this lens. Lastly I have never seen Epsilon Lyrae like I did tonight. Those airy discs were beyond perfect. Absolutely stunning.
Pi Aqulae one of my favorites was not only brighter but the darkness between the pairs was easily more pronounced. The seeing conditions were close to 8-9/10. Some slight softening every moment or so like the focus was drifting was evident. I felt like if it had just got to a 9+/10 I could've seen white ovals if any were present in the polar regions of Jupiter. Well that's enough rambling for now. Tomorrow nights forecast doesn't sound promising. We'll just have to wait for my DSO in Pegasus another night. Oh I forgot to mention Vega! There is CA but nowhere near what the Jaegers or the Brandt showed. The Brandt had it's usual bluish purple. The istar not only was it's usual lavender purple but Vega itself was a white. In the Brandt there was a yellowish white look. Delta Gygnae never showed the companion better. The secondary was a pin *BLEEP* lavender star...beautiful to say the least.
● Replacement refractor on Mt. Sromlo Observatory, Australia. / iStar Optical 220mm F/15 Achromatic Doublet
by Tim Wetherrel
Finally got chance to test the telescope on some terrestrial targets late in the day and the news is all good! The day was a bit hazy so we used a tree about 200m away as a target to cut out atmospheric effects as much as possible. Was very impressed with the lens, it created sharp contrasty images just as one would expect from a good quality large refractor. Using the 65mm wide angle eyepiece it was quite spectacular. When you get to higher magnifications 250x upwards there's a slight violet halo at the edge of branches just as you'd expect from an achromat but the image remained crisp and true. We wound the magnification up to 550x with a 6mm ethos without any real degradation except a little false color, which I'd imagine a minus violet filter would completely eliminate - just didn't have one handy. So in short, I'm very happy with the lens. We'll do some testing on artificial stars when we get the chance but I can tell just from the quality of the terrestrial images that it's a really nice lens.
● Perseus AT 210-9
by James Ling, Malaysia
Here are my little comments that I want to tell both of you with regards to the 8" iStar achro performance, for the night… whereby is a bit cloudy , and cooling night, as there is heavy clouds in the day... (strange no dew till the morning)
1. M57 is of much better contrast then my Ultima 8" at 200x which I have been watching for the 2 past weeks, outside my home.
2. M31 this time, is much better than the view I seen through my C14, at the same place, a year ago... The background stars are clear when I only use a TV 55mm eyepiece, on this 1800 mm scope. The contrast on M31 is no longer just a blob of light I seen previously.
3. Jupiter is the best, as compared to my previous 2 observation, at the same place, although this time it did not shine brightly due to thin layer of clouds. Jupiter can only power up to 225X with my Baader planetarium 8mm to 24mm zoom eyepiece. My 9mm Nagler eyepiece shows the best view at 200. Surprising, through visual, the CA is not noticeable this time, perhaps due to the sky condition is not a very clear night...
4. M6, 7, 8 and M44 are great, when seen through this scope...
5. It splits the double-double easily near Vega...
6. Albireo double stars is so beautiful, if the person is not an experience triplet guy, no one will ask why the 4 points star like has two color, red on one plane and blue on the other...
7. M42 and the trapezium are easily seen, although the sky is not very clear even during the moment of good seeing...
James Ling, Malaysia
● iStar Optical 204mm F/11.7 Achro
First light report by Leslie Hess, Arkansas, USA
I am proud to say that I now own one of only a handful of 204mm f11.7 achro lenses produced by iStar Optical. After much discussion and considerable deliberation I settled on this lens for my ultimate scope, initially I had decided on the 6 inch f15 objective and even placed the order. However, I changed my mind and contacted iStar the next day to change the order. iStar agreed to produce a single lens. This is not normal stock for iStar, but the single lens was produced at no extra charge. It was delivered on time in about 6 weeks. I cannot stress enough how superb iStar customer service is.
I have been an optics-geek since I was a kid. About 10 years ago I built my first entry level scope. A 10 inch Dob which I used for several years.
As I unpacked the lens it proved to be in perfect condition. The coatings were beautiful and flawless. Initial star tests showed no coma or astigmatism and had good surface quality. The lens was slightly over-corrected which is fine with me as it proved not to be an issue. Quality of the lens overall is quite good.
After months of constructing my OTA, I was finally ready to test in the real world. I double checked the OTA collimation to ensure all was square, mounted the 7 foot assembly to the base and waited for dark. Cloud cover was clearing and I was hopeful for a triple play.
The eyepieces I used are the ones I use in every scope I own. This eyepiece set includes the Russell Optics 11mm swa, 32mm konig, 19mm uwa, and my cheap 2x Barlow.
Before the moon rose I had a break in the low cloud cover to get a clear view of M42. Absolutely the best view I have ever seen, bar none. The young star cluster tightly grouped so perfectly even the 5th faint star in the tight 4 star cluster was easily resolved. I saw more detail in the cloud itself than ever before. Absolutely no coma or astigmatism was present leaving superb contrast. Only the brightest stars in the sky had slight chromatic aberration, which could be due to the cheap eyepieces I was using.
The star test proved to be dead on. The lack of chromatic aberration, coma and astigmatism conspired to make this a genuine joy. I have to keep reminding myself that this is an f12 scope!
A cloud bank rolled in and took an hour to clear. By this time the moon was at about 40 degrees high. This scope is so eager to magnify. The 2400mm focal length and the 11mm barlowed by 2X yielded 430X. Boy does it add up fast. The moon was at 98 percent full; I had one cratered edge to enjoy. With the 32mm, the moon was gigantic, super sharp and totally CA free edge to edge. With the 11mm the detail really began to pop out, now we are getting down to business. I added the Barlow and pushed very high power. Sky conditions were far from ideal but the clarity, sharpness, contrast and total lack of CA blew me away. I am positive this instrument would have yielded much higher useful magnification but I ran out of sky and eyepiece possibilities. The clouds rolled in. Unfortunately, it was cloudy by the time Saturn rose.
I made the perfect choice for my purpose and would purchase this lens again. Within the last 12 months I looked through a 24 inch truss reflector, 8 and 10 inch dobs and several large aperture compound scopes. This 204mm objective most closely compares to a 14 inch compound scope. I ended up with a superb telescope and look forward to years of use.
Fast forward a couple of weeks and I have finished the scope and mount. I am taking off work Monday to see Saturn and report to my friends here at Cloudynights. But the clouds rolled in again the same as last time.
-- Leslie Hess
● iStar Optical 150mm F/15 Achromatic Doublet in Cell
First light report by Eden Orion, Israel
Two days ago I've tested my 6"/15 scope for the first time. As I've wrote before I've tested it before, just to see the correct place for the lens. But the night before yesterday was the first real test.
Before the test I did (With my son) the collimation process . In the book "Build your own telescope" the process was described well but It looked to me, after years of using laser collimators on Reflectors not so accurate...
Well, After four of my friends, each one of them have "some" experience with Telescopes (all kinds of) the final verdict was "pinpoint sharp".
Moon was fantastic. almost fool with a lot of details on its face , thanks to the wonderful contrast of such scope. Jupiter was AMAZING, very sharp with a lot of true colors of the belts and some ore details with am 26 mm eyepiece.
With an 14 mm eyepiece, Albireo was spread for a noticeable part of the field with it's blue and yellow stars like pin-points.
Now I'll go into the painting job. I think it will take another two weeks or so.
● Comment posted on Cloudy Nights
September 2010, by Leslie Hess, Arkansas, USA
I have been looking for larger retractor lens for some time now. I found the iStar and here on CN and did some research on the company and found nothing but good. Some impressive builds have already been documented. I really joined up because of Sean’s Jill build.
I decided on which lens to purchase. I know aperture and fl are what I am after plus acceptable lens quality. I contacted Ales at iStar via email. I really expected a generic response like we have all become accustomed to. Generic was not what I got.
I must have asked a hundred questions and I must say Ales answered every single one of them. Not a single email of a dozen or so went unanswered. I wish all companies could deliver service like iStar and Ales and Gay on the Arizona side.
After ordering the 6 inch f/15 I had reread the volume of emails I received from Ales. I ended up changing my order to the 8 inch f/11.7. iStar is making a single lens production run at no additional cost as this lens is not normal stock. I am stoked. Eta 45 days.
Rock on iStar.
● Perseus AT 150-10 OTA report
by Steve, Darwin, Australia
Ales has done it again.
Last week I received this beauty, delivered to my door. The packing was superb and it arrived in perfect condition. This is hugely important to prospective buyers. I have included a photo of packing. I received lens and focuser separately. Equally well packed.
Putting together was simple. Fit and finish excellent. The machining is a work of art. The scope is completely CNC machined. Even the holes are CNC made!!
I wanted this scope baffled for higher magnifications. The baffles are all bolted in, no glue. Very solid.
I went for the F10 as the best compromise (IMO) between size, mounting and optical performance.
1st light was a delight. The correction is about as perfect as I have seen with any telescope. Everything lined up perfectly. Jupiter was on hand for some critical viewing and it did not disappoint. Resolution excellent and CA very unobtrusive.
Considering the price, this is one great buy.
Well done iStar.
PS I ordered the 3.5" focuser which is a delight to use but I believe Ales will not be selling anymore of these, which is a shame.