Re: (IAAC) FWD: What should I buy? (rich field scopes)
Gee, well they weren't apparent to me or the other two observers who
were doing comparisons with me. The sum of our observing experience totals
over 80 years. I guess we still don't know how to do it right.
The transmission of the Naglers is a few percent less - an amount not
very noticeable to humans who sense light according to a power law. Since
more of the light goes where it belongs in the Nagler, the point is somewhat
If you think that Orthos are better corrected across the field than
Naglers, I suggest you look at the ray trace results for eyepieces in
"Telescope Optics, Evaluation and Design" by Rutten and Van Venrooij.
I don't own any fast scopes, my Naglers are my higher power eyepieces,
and most of my scopes are driven.
I'm not claiming that I can't detect any internal reflections in the
Naglers. I'm just getting very tired of hearing people say how terribly
obvious their flaws are, as though Naglers are unsuitable for critical work.
As for Orthos, the off-axis images go to hell in a hand-basket, and not all
objects that profit from critical study are minute in diameter. With Orthos
you also have to decide whether you would rather put up with their
astigmatism or the trade-off field distortion of the Naglers.
Clear skies, Sue
>If internal reflections in the Naglers are not obvious to you, you aren't
>Since the light transmission of Naglers is a few percent less than the
>Orthos, and the design is not as well corrected as orthos across the field,
>it may seem that the Nagler is "sharper, brighter, and clearer" than a good
>ortho - especially at low power on a fast scope, where other aberrations
>will overwhelm the correction of the ortho - but in reality the perception
>is nothing but fantasy.