This short focal length Celestron Ultima LX is an excellent high power eyepiece with a very wide 70° field of view. It is outstanding for medium magnification viewing with short focal length refractors and fast focal ratio/short focal length Dobsonian reflectors. It is also an excellent choice for high magnification observing with long focal length refractors, reflectors, or catadioptric scopes under good to somewhat better than average seeing conditions. Below average
seeing conditions may limit its performance with the latter scopes, however. If so-so
seeing is the norm where you observe, its 8mm focal length may represent the maximum practical with a long focal length scope.
With a usable eye relief of 16mm (quite long for an eyepiece of this focal length), the 8mm Ultima LX will provide nearly unvignetted views for most eyeglass wearers, although some vignetting is unavoidable if you must wear eyeglass while observing due to severe astigmatism. There is a slight loss of contrast when compared to an eyepiece with fewer elements, due to the additional lenses needed to achieve the unique combination of very short focal length and very generous field. The loss is minimal though, on a par with the contrast loss in an eyepiece/Barlow combination with the same effective very short focal length.
Dual concentric barrels let you use this eyepiece in either a 1.25” star diagonal/focuser or a 2” star diagonal/focuser.
At 22 ounces and 5.4" long, the 8mm Ultima LX is a very substantial eyepiece. Be sure that your star diagonal is very firmly locked in place in your scope on your scope before inserting this eyepiece to avoid the chance of the diagonal swiveling unexpectedly and the eyepiece falling to the ground.
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