| Exceptionally long eye relief for eyeglass use is the hallmark of this short focal length 6mm Vixen Lanthanum eyepiece. The 6mm Vixen uses seven optical elements in four groups to achieve high power without reducing its eyeglass-friendly 20mm eye relief. This 6mm Vixen eyepiece is designed for unvignetted medium to medium high magnification viewing with short focal length refractors and fast focal ratio/short focal length reflectors. It provides a 1mm exit pupil with f/6 refractors and reflectors, the exit pupil value that typically provides the most lunar and planetary detail with any given f/6 scope on nights of average to good seeing conditions. It is starting to get into the range of being more or less regularly useful with long focal length refractors, reflectors, or catadioptric scopes (Schmidt- and Maksutov-Cassegrains) under good or better seeing conditions. While this eyepiece can perform well with these long focal length/long focal ratio scopes, don’t expect it to do so every night. Merely average seeing conditions (the kind you’ll experience most nights) will still limit its performance. The optical performance is quite good for a short focal length eyepiece, on a par with that of a good Plössl. There is a slight loss of contrast when compared to a Plössl, due to the additional optical elements needed to achieve the long eye relief of this Vixen. The loss is minimal though, and this Vixen still has the benefit of much longer and more comfortable eye relief at a cost half that of other 20mm eye relief eyepieces. | 
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