This is a superb short focal length ultra wide field eyepiece designed as an upgrade to the original and highly-prized 7mm Nagler. Due to the significant cost increase of this latest version over the original 7mm, the original 7mm Nagler will continue to be available for those who wish a lower cost alternative to competitive designs that are based on the original Nagler optical formulation.
This 1.25" eyepiece uses seven optical elements for optimized performance across a very wide field of view. Several different extra low dispersion glass types and specialized coatings are employed for improved contrast and longer eye relief than previous Nagler designs, even those acclaimed as being among the finest wide field eyepieces available. At a usable eye relief of 12mm, the 7mm Nagler would normally vignette the field of view for eyeglass wearers. However, since the 82° field is so wide that you can't see the full field without having to move your head from side to side to take it all in anyway, vignetting in the conventional sense is not a problem.
The optical performance is typical TeleVue - well corrected and sharp from edge to edge. There is a slight loss of contrast when compared to an eyepiece with fewer elements, due to the additional lenses needed to achieve the unique combination of very short focal length and very wide field. The loss is minimal though, on a par with the contrast loss in an eyepiece/Barlow combination with the same effective focal length. In the eyes of many observers, however, the "picture window on space" observing experience of its exceptionally wide field more than makes up for any slight contrast loss.
Supplied plastic caps seal both ends of the eyepiece to keep it dust free. A rubber grip ring gives a secure and comfortable grip in all temperature extremes. A groove machined into the chrome barrel of the eyepiece acts as a safety stop to keep the eyepiece secure should the focuser thumbscrew loosen slightly while using the eyepiece.
