| This Astro-Tech 10mm Titan is a very wide 70° field medium to medium-high power 1.25" eyepiece at a very economical price. Its 10mm focal length makes it a good choice for high power lunar/planetary observing and binary star splitting with a long focal length telescope. For instance, with an 8" f/10 catadioptric, it provides 200x with a 1mm exit pupil, the optimum exit pupil generally recommended to best match the resolution of your telescope to the resolution of your eye. The field of view with such an 8" f/10 scope is a surprising 0.35° at 200x, nearly three-quarters the lunar diameter. With short focal length refractors and fast focal ratio reflectors, it makes globular clusters and compact nebulas vivid and nearly three-dimensional. A f/4 Meade 8" Schmidt-Newtonian reflector, for example, yields a 2.5mm exit pupil, 81x, and a generous 0.86° field of view that’s perfect for globular clusters like M9, M13, and M22. All fit nicely into the eyepiece field of view, with a framework of black velvet sky around them to set off their subtleties. The 66mm f/6 Astro-Tech AT-66 refractor, on the other hand, has a magnification of 40x with this eyepiece, with a 1.66mm exit pupil and a generous 1.75° field (three and a half times as wide as the full Moon). That wide field is good for observing open clusters such as the Pleiades and the Double Cluster in Perseus; 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 framework of black velvet sky around them to set off their subtleties. The 7mm eye relief is somewhat short for those who must wear eyeglasses while observing due to astigmatism, and will somewhat vignette the field. This is of minor concern, as even those who don’t have to wear glasses while observing will find they have to move their head from side to side while observing to see the entire huge field of view.
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