Quote:

---

I read somewhere that with UWA EPs you cant go longer than 25mm focal lengths. Is this true?

---

Actually, using Denk BVers as a reference, 24mm SWA (~68*) EPs can in some scopes be a stretch- Denks own SWA EPs being 21mm/65* AFoV. I'd guess that somewhere around ~18mm FL would be the max in an "UWA" (ie. 82*) EP for a Denk-type BVer... and even shorter FLs for the above in a smaller-prism'd BVer make.

To add a touchy-feely aspect to David's above description of "vignetting", what you'd *see* in the EP would be a gradual darkening toward the outer FoV, growing darker toward the edges. Stars in a uniform starfield would begin dimming & snuffing out as you viewed toward the edges, fainter ones first, etc. Instead of a definably hard, crisp field-stop edge to your view, you'd see a vague & fuzzy *zone*.

When one is used to the crisp edge to a view, bounded by blackest black, the vignetted view is like wearing clothing of the wrong size- its quite distracting & bothersome.
mike b

--------------------
Welcome to 2009!

May your skies, your mind, and your heart all be steady & clear!

* * 15" F4.55 Starsplitter Dob * *

Pacheco State Park
Fremont Peak

Post Extras