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

[Michael Gregory <mikeg@airmail.net>]

Scott,

    The full mirror is visible in the Vixen.  I recently painted the outer
2mm or so flat black.  The weather here has not been very cooperative
lately, but I did take a few CCD images.  It appears that masking the 
outer edge did reduce the halo effect around bright stars.  The clips
extend about 1/4 inch into the primary area.  I didn't mask nearly
that much, and the clip induced shadows are still there -- maybe 
reduced somewhat.

Regards,

Mike.


At 10:54 AM 2/10/01 -0600, you wrote:
>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.

>
>Keep lookin up!
>
>Scott B.


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