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It is designed for unvignetted very high magnification viewing with short focal length refractors and fast focal ratio/short focal length reflectors. While it can also be used with longer focal ratio Schmidt-Cassegrains and Maksutov-Cassegrains, its exit pupil becomes prohibitively small and the images very dim with these scopes. For example, using it with a 2000mm 8” f/10 Schmidt-Cassegrain will result in 800x (100x per inch of aperture) and a 0.25mm exit pupil (about 1/100th of an inch across). Both of these figures far exceed the rule of thumb maximum values of 50-60x per inch of aperture and a 0.5mm exit pupil for usable observing under good to very good seeing conditions for a reasonably experienced observer.

Its rubber-clad body gives a sure and comfortable grip in all temperature extremes. The optical performance is very respectable, on a par with that of a good Plössl, although there are no Plössls available in this exceptionally short focal length. There is a slight loss of contrast when compared to a Plössl alone, due to the additional optical elements needed to achieve the unique combination of very short focal length and very long eye relief of this Vixen. The loss is minimal though, on a par with the contrast loss in a Plössl/Barlow combination with the same effective focal length, and this Vixen would still have much longer eye relief. Given the constraints of its inherent high magnification and the typical seeing conditions, this Vixen should be considered more for its virtue as an eyeglass-friendly eyepiece (particularly at a price half that of other 20mm eye relief eyepieces in this focal length range), rather than for any special optical excellence.

Due to the long 3.25” length of the eyepiece, optional eyepiece case #EPA will seal most effectively if the foam piece in the bottom of the case is removed for storing the eyepiece.