This wide field Pentax eyepiece is designed for high power observing of objects on the ground by day and in the skies at night.
Terrestrially, it is the most powerful eyepiece usable for nature studies with the 80mm and 100mm Pentax spotting scopes under brightly lit observing conditions.
Astronomically, it’s an excellent choice for high power lunar and planetary observing with long focal length refractors, reflectors, or catadioptric scopes under good to somewhat better than average seeing conditions. It is also exceptional for medium power viewing with short focal length refractors and fast focal ratio Dobsonian reflectors. It has eight lenses in a six group optical design. This gives a sharpness across its very wide 70° field that makes smaller globular clusters vivid and nearly three-dimensional. It is also more or less regularly useful for astronomical observing with long focal length telescopes, but below average seeing conditions will limit its performance. If so-so seeing is the norm where you observe, its 7mm focal length may represent the maximum practical with a long focal length scope.
The long 20mm eye relief is ideal for those who must wear eyeglasses while observing due to astigmatism. Even those who do not wear glasses will find the long eye relief a comfortable change from the cramped eye relief that is typical of the usual short focal length eyepiece.
For terrestrial observing . . .
With an 80mm straight-through Pentax spotting scope this eyepiece provides 71x magnification and a 52’ field of view at 1000 yards, which are the values given in the specifications to the left.
With the 80mm angled Pentax spotting scope this eyepiece provides 74x magnification and a 50’ field of view at 1000 yards.
With the 100mm aperture Pentax spotting scope this eyepiece provides 90x magnification and a 41’ field of view.
In all cases the spotting scope exit pupil will be in the neighborhood of 1mm, providing somewhat dim images if the scene being observed is not brightly lit.
For astronomical observing . . .
The field of view of 70° degrees given in the specifications to the left is the apparent field of view. The actual field of view will be equal to that apparent field divided by the magnification of the eyepiece/telescope combination.
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