Re: ATM Re: Why?

[Bill Marriott <btk@pacbell.net>]

Suzy Jackson wrote:
The autocollimation null, while
> desirable, is out of my reach because I don't have a large flat (indeed I
> don't have a large apartment either, but that's another story), and from my
> readings I don't fancy my chances of making one either.  
Though jumping in late on this thread, I thought I would note the
following, as to reasons why an autocollimation setup  is not beyond the
reach of a reasonably talented ATM'r.

It has been previously noted on this list, and are buried in the
archives somewhere that:

The autocollimation flat does not need to be 'that' flat, somewhere in
the archives is a formula that gives the the wave rating for a given
diameter and f-ratio, and is surpassingly very liberal, as long as the
figure is smoothly spherical.

Also, one does not need the classical 'bigger than your primary' size
flat, as long as the flat allows one to test the center to edge zones of
the system. Either the primary or the secondary can be rotated in this
setup to check for astigmatism. So, say for a 12" mirror, a 8" flat may
be used, a 10" would be better. I have done this, and it does work,
though requires a little more effort.

One reporter's opinion

Bill 'yes, I'm still around, but busy' Marriott
http://www.starlightoptical.com