Astro-Tech 5.5mm 1.25" PF Eyepiece

This Astro-Tech 5.5mm PF eyepiece is excellent for medium to medium high magnification viewing with short to medium focal length refractors and reflectors. It is also usable with long focal length refractors and catadioptric scopes under good or better seeing conditions.

Average seeing conditions will limit its usefulness with long focal length scopes due to the inherent high magnification of its 5mm focal length. Using it with a 2000mm 8" f/10 catadioptric, for example, will result in 363x (45x per inch of aperture) and a 0.5mm exit pupil (about 1/50th of an inch across). Both of these are just under rule of thumb limits for maximum magnification per inch of aperture and minimum exit pupil size for usable observing under good to very good seeing conditions for a reasonably experienced observer.

The six lens/four group design of the 5.5mm Astro-Tech PF provides all of the optical virtues described at the top of this catalog page - high contrast, a sharp and flat field from edge to edge, excellent color fidelity, and exceptionally low astigmatism and barrel distortion. It has a usable eye relief of 16mm, excellent for such a short focal length eyepiece. The eyepiece some with a traditional rubber fold down eye cup to assist that glasses wearers of the world find a comfortable eye position.  This particular eyepiece has a nice 60° apparent field of view.

Enjoy the night skies with this very reasonably priced premium eyepiece.