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Siebert 22.5mm Ultra Plus

Started by DrThud, 08/14/2002 08:34PM
Posted 08/14/2002 08:34PM Opening Post
(From Ryan A.'s query in "Equipment" forumsmile

This was the first & only 22.5mm U.P. I've seen in the field. They're still quite new & rare.

This is not a review. I'll note impressions of the eyepiece & the view it yielded, but I'm working from memory. No A-B comparing was done. I'm still largely unfamiliar with both the eyepiece & the scope it fed. Keep grains of salt handy :-)

The eyepiece: a 1.25-inch 22.5mm Ultra Plus, Harry's latest design, uses a stainless steel barrel/body & hard slide-fit eyecup sleeve. The sleeve fit snugly around the body (no slop). "Below" the sleeve was a beefy twin o-ring, functioning (I think) as barrel stop &/or sleeve stop (user's choice). Sleeve was snug enough that my own preference would be to use the ring as barrel stop (parfocal with another eyepiece).

Being Edmund-sourced, the lenses' polish & coatings appeared superb.

The views: I think of the 22.5mm U.P. as a 60-degree, long-eye-relief, widefield orthoscopic. The owner's scope is a Nexstar 80GT (*very* fast & designed for wide fields @ moderate magnification). In the 80GT, the 22.5 yields ~18x over a ~3.3-deg. field. Over two nights, it fed on brighter Messier & NGC clusters, nebulae, & galaxies. I peeked at maybe 20ish, including Ms 7, 8, 11, 13, 16, 17, 20, 31, 45, 57, NGC 6992, Double Cluster, & more. At no time was I unimpressed by the U.P. Yes, the combo yielded some off-axis astigmatism (expected). However, the image "sweet spot" was robust, perhaps the central ~70% zone. Tight, hard, stars within; reasonable astigmatism beyond (akin to my Meade SW at ~f/7). No rabid seagulls; o-a astigmatism well controlled, given the f/5 system. I'm astigmatic myself; not sure how much (if any) my eyes contributed to the astigmatism seen.

No vignetting. No black-outs. No kidney beans. Can't comment on lateral color or induced chroma (no benchmarks for comparison).

Nutshell: I like the 22.5mm Ultra Plus & want to see more of it. When I do, I'll pay more attention, make comparisons, & take notes.

Hope this babble wasn't vague or useless. If any specific ??s, let me know.

Best wishes.
-Dan