Re: 2" 90° Apparent Field Eyepieces Announced

From: brian (brianc1959_at_aol.com)
Date: 07/03/04 

Date: 2 Jul 2004 20:11:49 -0700

rander3127@rogers.com (Richard) wrote in message news:<ec75e55a.0407021345.277974e8@posting.google.com>...

>
> Big waste of time, size and money when ED glasses can be bought now.
> I can just see those poor refractor and Newtonian owners trying to balance
> that thing, once they had a 4" focuser that is.
> -Rich
> -Rich

Rich:
ED glass is nearly useless in eyepieces due to the relatively small
marginal ray heights. At best you could use it to modify the
secondary lateral color and secondary chromatic variation of
distortion, but you'd better be sure that these are actually the
limiting aberrations. The "integral Barlow" type design used in the
Dilworth and Nagler eyepieces helps mainly to correct astigmatism and
field curvature to an extraordinary degree over a very wide FOV. The
cost of this performance is size and weight.

Brian
www.caldwellphotographic.com