Frequently Asked Questions



Is vignetting normal in most optical reducers?

   Yes, he vignetting is perfectly normal.  When optical designs state an image circle, that means that the stars are corrected and sharp over that circle, but it does not mean that circle is fully illuminated.  That is almost never the case with any optical system.  Pretty much all focal reducers on any scope will show vignetting.  The Apex flattener-reducer will show some vignetting but proper flat field images will perfectly remove it.  Be sure to take bias frames or flat darks along with the flats in order to properly calibrate them.  But that will do the trick!


Is it true that long focus Achromats can offer superior images to short focus Apochromats?

   Read this well researched article by Neil English and make up your own mind.


Is there a charge for cancellation of my  preorder?

   Unfortunately, we cannot accept cancellation on custom ordered products as this order was produced specifically for you. Unforeseen occurrence may delay your shipment. We strive to deliver in a timely manner. If you placed an order for a “stock” item and you need to cancel, there will be a 10% charge calculated from the total retail price of the item that will be retained by us. We produce in limited quantities resulting in most units being sold before we take delivery from production.


What does the term “Average Strehl” value mean?

   Average Strehl (SR) is a monochromatic Strehl value measured in one single wavelength at 510nm (Green) and then adjusted (lowered) by the average production tolerance value.


Will iStar Optical ship any product with lower value on the invoice?

   iStar is known for its excellent and friendly customer service. While we will go to great lengths for you, falsifying some information on shipping invoices or import documents is not one of them. We will only provide accurate documentation for the import of telescopes, lenses and accessories. Please do not ask us to undervalue our merchandise in order to save on import taxes. It is against the law in every country we ship to. Selling telescopes is our livelihood and we cannot jeopardize that. We greatly appreciate your understanding in this matter.


Why choose a refractor?

   Ask anybody to describe a telescope and the image of a long tube and lens at the end will be their answer. Except for the diagonal, which makes possible viewing at a comfortable angle, there are no mirrors to scatter and lose light. There is no central obstruction, no frequent collimation to worry about and very reasonable cool down time. How about sharp, high contrast views of the Moon and planets? If you like black velvety backgrounds with pin point stars, a refractor is for you.


Why a long focal length?

   Using long focal lengths puts large aperture refractors within reach of most amateurs. Most people associate inexpensive achromatic lenses with horrendous amounts of false color (chromatic aberration). Not so with longer focal lengths. When the focal length is increased in relation to the aperture the inherent aberrations associated with achromats are minimized. Another advantage is depth of focus. No constantly tweaking the focus. Greater depth of focus allows a steady, comfortable viewing experience especially when observing the Moon, planets and double stars.


What is a Bare OTA?

   iStar Optical does not offer mass produced telescopes with non-replaceable focusers, low quality rings and dovetails. Instead, we offer you the option to purchase a bare OTA with optics and give you a choice of focusers, mounting rings and dovetail. You do not have to purchase these from iStar. You are welcome to buy from third party manufacturers. However, we offer the original iStar PRO style rings and dovetails that are of the highest quality, stability and match each scope perfectly.


What is an R30 or R60 doublet?

   iStar Optical uses special exotic glass types to achieve 30 to 60 percent reduction in CA and spot size compared to a common doublet made with popular less expensive glass types.


iStar Optical Lens Caps

   We ship all scopes with a specially designed lens cap. You can decrease or increase friction inside of the dew shield by loosening or tightening the two silver bolts. When you tighten them the diameter of the foam ring will increase therefore increasing the friction inside the dew shield. They look unlike any other lens cap on the market and of course and they work better than any other lens cap.


How can I fix a scratch on my iStar Optical scope tube?

   iStar Optical tubes are powder coated. However, a “quality” black matte spray paint can be used to cover a scratch. The paint sprayed over top of the powder coat will take on the texture of the original finish. Use only as much paint as is necessary to cover the scratch. After drying the paint should have blended well.


Concerning the R30 and R65 products. What is the actual effect of a 35% or 65% reduction in CA?

   Generally the effect of a 35% or 65% reduction in CA is smaller SPOT size. For example, the R65 lens should have about the same amount of false color as a scope with a 65% longer focal length, or about the same as an F/8.25.


Why is the price on the iStar Optical Web site less than my US dealer?

   Scopes ordered directly from iStar are at present shipped from the Czech Republic in Europe and do not have DHL shipping charges or import taxes added.


Are iStar Optical telescopes produced in China?

  Absolutely not! iStar’s mechanical and optical designs are created in the Czech Republic, Europe. All of our lenses were designed by Master Optician Zdenek. The telescopes and related parts were designed by the owner of iStar, Ales Krivanek. Telescope tubes and dew shields are produced in Austria and CNC machined and powder coated in the Czech Republic. Scopes are assembled by hand and tested in the Czech Republic and the United States. Currently all materials used are of European origin with the exception of focusers that are made in the US. A major expansion will take place in 2012 with most manufacturing and assembly being moved to the United States. Lenses are ground and polished in Asia to iStar’s exact quality specifications and exported to the US to be mounted and shipped worldwide. Only brand name glass from O’Hara, Schott and CDGM is used.


Is the iStar Optical Perseus line of achromatic doublets suitable for astro-photography?

   Yes. iStar lenses are made to meet high quality standards. Many knowledgeable and experienced astronomers have made it clear that even though these instruments have only a modified Fraunhofer (air spaced achromatic doublet) in them, they are suitable for a good quality Moon, planetary and DSO photography. Incredible results with pinpoint starts and vivid colors have been achieved with use of a narrowband filter.


Is the iStar Optical Phantom line of telescopes made with CaF2 or simple Fluorite glass?

  There are many manufacturers offering so called Fluoro-Star, Fluoro-Triplet and Fluorite Triplet Glass to make buyers believe their instrument is made with a pure fluorite element. Calcium Fluorite is the best optical material on the market today in terms of color correction. It is also the most expensive. All Phantom CFT telescopes are made with pure crystallized Calcium Fluorite, CaF2. There are very few manufacturers that produce scopes made with this rare material. Images taken with CaF2 triplets are in class by themselves and are rightfully considered to be the very best among knowledgeable astro photographers. Have you viewed a DSO or planetary image taken with a Phantom CFT scope? If you did, you are probably saving your money to purchase one.