| This 2.5mm TMB Planetary eyepiece from TMB Optical gives you exceptional high power views with short focal length/fast focal ratio refractors and reflectors – even under so-so seeing conditions. It has been optimized to view bright objects, both on and off axis, while showing maximum detail and definition. The TMB has very high light transmission, very high contrast, minimal lateral color, and minimal light scatter.
The very short focal length 2.5mm TMB will work with f/8 reflectors and f/10 catadioptric scopes, but its tiny exit pupil (0.3mm with an f/8 scope and 0.25mm with an f/10) and very dim images with such scopes make it exceedingly difficult to use.
Combine the 2.5mm TMB’s 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 f/5 or f/6 focal ratio telescope. Its 2.5mm focal length provides 192x (a very high 62x per inch of aperture) with an 80mm f/6 refractor, about the practical maximum magnification possible under very good seeing conditions. While this TMB eyepiece is optimized for observing subtle lunar and planetary detail and low contrast features, it works equally well for splitting binary stars, resolving compact globular clusters, etc. An 80mm refractor would be about the smallest aperture scope recommended with this eyepiece; refractor apertures of 100mm and larger would be preferable.
Eye relief, at a surprising 14mm, is exceptionally good for an eyepiece with such a short focal length. Vignetting will be relatively minor for those who must wear eyeglasses while observing. This usually won’t be a problem when using the TMB Planetary eyepiece on the kinds of objects for which it was optimized – planets, binary stars, etc. – as these small objects are generally kept in the center of the eyepiece field, where your eyesight is sharpest.
For Dobsonian users and others without tracking drives, the very low lateral color and other aberrations allow a planet to drift across the entire 58° field while still being sharp and having high contrast, thereby maximizing your observing time.
A light coating of lubricant has been applied to the threads of the twist-up eyecup. If any lubricant is visible on the inner eyepiece body when the 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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