Product Description
The 3.5mm Nagler is designed for high magnification observing 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 is very small and the images very dim with these scopes. For example, using it with a 2000mm 8" f/10 Schmidt-Cassegrain will result in 571x (71x per inch of aperture) and a 0.35mm exit pupil (about 1/90th of an inch across). Both of these figures exceed the rule of thumb maximum values of 50-60x per inch of aperture and a 0.5mm exit pupil for usable observing and would require exceptional seeing conditions to be usable.
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 of this Nagler. 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.
Tech Details
Barrel Size | 1.25" |
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Eye Relief | 12mm |
Field of view | 82 |
Focal Length | 3.5mm |
Number of optical elements | 7 |
Weight | 8.6 oz |
Warranty | Limited Lifetime |