Re: ATM building a finder

["Bob May" <bobmay@nethere.com>]

Yep, Petzval curvature is a lot higher one way than the other.
Petzval curvature is the curvature of the focal plane and is generated by
any curved surface.  You can change the Petzval curvature by changine the
bending of the lenses as a set.  You just found out that by bending the
lens, you have changed the Petzval curvature.  You did this by putting the
lens in both ways, one direction of which had the lens bent forward, away
from the eyepiece, (consider that the lens is flat on one side and strongly
curved on the other so take the average of those two curves as the basic
curvature of the lens) and the other direction the lens is bent towards the
eyepiece.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net