Re: [APML] Novak cells, clip diffraction patterns (was Alnitak)

[Scott Barbee <sbarbee@centurytel.net>]

If your full mirror is visible, without any baffles, then you could have a
diffraction pattern caused by the edge of your primary, which is what I have with
mine, and I'm putting a mask over the outer 1/4" of my primary. My primary has a
"beveled edge" which is causing these strange, but interesting patterns, see:

http://www.geocities.com/cloudchaser57/astropics/m45done.jpg

This was brought up several months back, and at that time I believe the consensus
was to mask the very outer edge of the primary. By the way, my secondary is very
large, 4" for an 11 3/8" primary. I have my mask made and scope in the house out
of my observatory, so hopefully I'll get it set soon and have results to compare.

By the way, anyone planning on getting the Space station in the next few nights?
For Wisconsin and northern Minnesota, the next two nights are good nights to view
it, at -1 mag. It only takes 10 min to pass from horizon to horizon, and from my
location, it will go right next to Jupiter and Saturn at about 6:25 central,
which would make a pretty neat pic! Hopefully I'll have clear enough skies to get
a shot off!

Keep lookin up!

Scott B.

Michael Gregory wrote:

> Bobby and Torsten,
>
>     The clips are flat black.   The R200SS has a large secondary
> (short focal length).  The entire mirror (with clips) is visible from the
> focuser.  Is that the case in each of your scopes, i.e. is the
> entire light cone (including the clips) visible?.  If so, how wide
> are the clips.  The Vixen clips are fairly wide.
>
> Thanks,
>
> Mike.
>
> At 03:48 PM 2/9/01 -0600, you wrote:
> >Whatever is the cause in the Vixen scope, the same effect is present in most
> >of Malin's photographs with the AAT. Check out his pics in his book or his
> >site.
> >Bobby Middleton
> >
> >From: Torsten Clay <tclay@theriver.com>
> >
> >> I have mirror clips on my 8" F/5 similar to Bobby's description. The
> >> mirror is actually glued in, but I leave the clips on for safety. I don't
> >> see effects like those from the Vixen either.
>
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