| Thomas M. Back, noted apochromatic refractor designer, has designed this short focal length eyepiece for exceptional medium high magnification observing with long focal length refractors, reflectors, or catadioptric scopes – even under average seeing conditions. It is 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. Its 9mm focal length is nearly ideal for an f/10 Schmidt-Cassegrain, as it provides a 0.9mm exit pupil that’s a close match to the 1mm exit pupil that most observers feel best matches the resolution of an SCT to the resolution of your eye. Combine that resolution with its high contrast and you have an eyepiece that’s unexcelled for lunar, planetary, and globular cluster observing with an SCT. (Some of the larger globular clusters, such as M13, will more than fill its 0.27 degree field with such a scope.) For Dobsonian users and others without tracking drives, the very low lateral color and other aberrations allow a planet to drift across the entire 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 globular clusters, showing subtle nebula contrast, 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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