| This medium focal length TeleVue Radian eyepiece is usable with any scope type, under virtually any seeing conditions – from fair to superb. An f/4.5 Dobsonian will yield a 3.1mm exit pupil, for bright images of emission nebulas and galaxies. With short focal length refractors, such as the TeleVues or TMBs, it’s a low power eyepiece. With the 600mm focal length TeleVue TV-85, for example, it provides 43x, a 2mm exit pupil, and a 1.4 degree field. With the 650mm focal length TMB-105 triplet apo, it provides 46x, a 2.25mm exit pupil, and a 1.3 degree field. On both scopes, the fields are almost three 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, and large globulars such as M-13. All will fit nicely into the field of view, with a framework of black velvet around them to set off their subtleties. With its long 20mm eye relief, even those who must wear eyeglasses while observing will see all of the wide field of this eyepiece and the splendors it can hold. It is also truly excellent for medium magnification lunar, planetary, and globular observing with long focal length refractors, reflectors, or catadioptric scopes. |
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