Re: ATM Effects of an inferior secondary

["Richard" <richas@earthlink.net>]

Even more interesting, what about diffraction?   For example, if an
undersized secondary limits an f/4 light cone down to f/7, does the
diffraction spot look like an f/7 light cone?   If the secondary is just
perfectly the same f/ratio as the primary, is there additional diffraction
from the secondary, and how does it add to that from the primary?

I know that in the past I have poo-pooed the worry over diffraction, but it
would be nice to understand how diffraction from various causes adds up.  I
am looking for some kind of fourier transform answer, not just platitudes
and rules of thumb from Nazi days of 1933 when commoners relied on the
authority of experts.

. . . Richard

----- Original Message -----
From: "Bill T." <twentiethwave@hotmail.com>
To: <atm@shore.net>
Sent: Thursday, July 19, 2001 4:13 PM
Subject: ATM Effects of an inferior secondary


>
> Speaking of secondaries, who can characterize the effects of a secondary
> that is less good than the primary?  What sort of defects does one see
with
> a crummy secondary, say on a star test?  Is it possible to sort out
> secondary defects versus primary defects at the eyepiece?
>
> Must primary and secondary PV ratings be matched for optimal performance?
> Can the secondary have a somewhat poorer PV rating than the mirror,
without
> image degradation?
>
> Bill T.
>
>