This medium focal length Pentax provides sharp and very wide field images for both terrestrial and astronomical observing.
Terrestrially, it is an excellent medium power wide field eyepiece for detailed close-in or wide field nature studies with the 80mm and 100mm Pentax spotting scopes in overcast and sub-par light conditions, dawn to dusk.
Astronomically, its six lens/four group design makes it an excellent high-contrast choice for medium power deep space observing with long focal length refractors, reflectors, or catadioptric scopes. It is a superb low power eyepiece with short focal length refractors and fast focal ratio reflectors. An f/4.5 Dobsonian reflector, for example, will yield a 4.4mm exit pupil, excellent for detailed images of emission nebulas and galaxies. Its sharpness across the field makes globular clusters and nebulas vivid and nearly three-dimensional. The 650mm focal length TMB-105 triplet apo refractor provides 32.5x, a 4mm exit pupil, and a 2.15-degree field (over four times as wide as the Moon). These figures are all very usable for observing open clusters such as the Pleiades; large nebulas such as the Lagoon, Veil, and Orion; and large globulars such as M-13 and Omega Centauri. All will fit nicely into the field of view, with a generous framework of black velvet sky around them to set off their subtleties.
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 25x magnification and a huge 147’ 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 26x magnification and a 141’ field of view at 1000 yards.
With the 100mm aperture Pentax spotting scope this eyepiece provides 32x magnification and a big 115’ field of view.
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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