With short focal length refractors and reflectors, it’s a low to medium power eyepiece. With an 80mm f/6 refractor, for example, it provides 28.2x and a huge 2.48° field that’s nearly five times as wide as the Moon. This is well suited for observing open clusters such as the Pleiades and large nebulas such as the Lagoon. Both will fit nicely into its spacious field, with a framework of black sky around them to set them off. An f/4.5 Dobsonian will yield a wide 3.8mm exit pupil, getting it into the low power rich field observing range.

It is also excellent for medium high magnification observing with long focal length refractors, reflectors, or catadioptric scopes. On a 14” Schmidt-Cassegrain, for example, it yields 230x. This is an excellent magnification for planetary and close-up lunar observing and binary star splitting.

With a usable eye relief of 16mm, the 17mm 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 an all-purpose medium 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 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 20 ounces, the 17mm 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.