For Replacement please consider Vixen - 4mm NLV Lanthanum Eyepiece
This 4mm TMB Planetary II eyepiece was designed to provide exceptional high power/comfortable eye relief observing with long focal length refractors, reflectors, or catadioptric scopes under average or better seeing conditions. It is optimized to view bright objects, both on and off axis, while showing maximum contrast, detail, and definition. It has very high light transmission, very high contrast, minimal lateral color, and minimal light scatter.
Combine the high resolution of the 4mm TMB Planetary II with its high contrast and you have an eyepiece that’s unexcelled for lunar and planetary observing and binary star splitting. While the 4mm TMB eyepiece is optimized for observing subtle lunar and planetary detail and contrast, the eyepiece works equally well for splitting close binary stars, resolving compact globular clusters, etc.
The 4mm focal length of this TMB Planetary II provides very probably the maximum power possible with an f/10 Schmidt-Cassegrain, as it gives a very high 62.5x per inch of aperture with such a scope. That’s more than the 50x-60x per inch of aperture considered the maximum possible under excellent seeing conditions. It provides the 0.5mm exit pupil recommended as the minimum usable for maximum detail with an f/8 focal ratio refractor or reflector.
Eye relief, at 10mm, is quite good for an eyepiece with such a short focal length. Vignetting will only be moderate for those who must wear eyeglasses while observing. This usually won’t be a problem when using the TMB Planetary II 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 of the 4mm TMB allow a planet to drift across its entire 58° field while still being sharp and having high contrast, thereby maximizing 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.