This Astro-Tech 5mm Paradigm Dual ED 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 400x (50x per inch of aperture) and a 0.5mm exit pupil (about 1/50th of an inch across). Both of these are right at the 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 and two ED (Extra-low Dispersion) glass elements of the 5mm Astro-Tech Paradigm 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 13mm, excellent for such a short focal length eyepiece. Combined with the twist-up eyecup design, the long eye relief makes it a good choice for eyeglass wearers.
This new Astro-Tech 5mm Paradigm Dual ED eyepiece will make you rethink your expectations about how much sheer short focal length eyepiece excellence you can get for such a reasonable price.
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