By limiting the field to 60 deg. (a Radian = 57.3 deg.) and establishing a uniform 20mm eye-relief, Tele Vue reworked the Nagler concept using the latest glass types to achieve optimum full field sharpness, freedom from distortion, freedom from ghosting (for critical planetary viewing) along with a unique adjustable eyeguard assembly which Tele Vue calls "Instadjust"
Instadjust was developed from the need for proper eye position for non-eyeglass wearers. It is essential, since with Radian's long eye-relief, non-eyeglass wearers would easily tend to get too close to the eyepiece, resulting in vignetting the field, just as you would moving out from the exit pupil. The click-stop, Instadjust eyeguard permits fast, accurate positioning of the eye to the exit-pupil with maximum suppression of environmental stray light. Instadjust is topped off by a soft (for comfort and eyeglass protection) fold-down rubber eyeguard and protective cap.
Usual Tele Vue features such as full multicoating, blackened lens edges, parfocalization, and grip-ring complement the Radian line.
Reviewed by 1 customers
A 3mm EP in my 4 1/2" F7 refractor puts the magnification right at the Dawes limit. So for me this EP is only useful during excellent seeing. That said - this EP provides a fantastic visual image. The surprising thing is that the image appears significantly larger in this EP than in other eyepieces I've had in this range. I saw the great red spot of Jupiter the other night, can't beat that. I'm not sure why most Radians are being discontinued, but this particular EP is a keeper.