| This short focal length eyepiece has been designed by Thomas M. Back, noted refractor designer. It is designed to give you exceptional high power views with short to medium focal length refractors and reflectors – even under so-so seeing conditions. It will work with f/10 catadioptric scopes, but its small half-millimeter exit pupil and dim images with such scopes will put it at the very limits of usability. It has been optimized to view bright objects, both on and off axis, while showing maximum detail and definition. It has very high light transmission, very high contrast, minimal lateral color, and minimal light scatter. Combine its high resolution with its high contrast and you have an eyepiece that’s unexcelled for lunar and planetary observing and binary star splitting with an SCT. Its 5mm focal length provides 400x (a very high 50x per inch of aperture) with an 8” SCT, about the practical maximum magnification possible under excellent seeing conditions. For Dobsonian users and others without tracking drives, the very low lateral color and other aberrations allow a planet to drift across the entire 60° field while still being sharp and having high contrast, thereby maximizing observing time. While the eyepiece is optimized for observing subtle lunar and planetary detail, the eyepiece’s observing virtues work equally well for splitting binary stars, resolving compact globular clusters, etc. A light coating of lubricant has been applied to the threads in the eyepiece’s twist-up eyecup. If any lubricant is visible on the inner eyepiece body when the twist-up eyecup is in the extended position, remove the excess lubricant with a clean wipe, such as a tissue. Operate the twist-up eyecup several times, cleaning the body as necessary until no more lubricant is visible on the eyepiece body when the twist-up eyecup is fully extended.
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