From: "Mike Spooner" 
To: "Rick Maillet" , 
Reply-To: "Mike Spooner" 


The mirror is stressed by the use of this many spots of RTV on a thin
mirror. Try a piece of masking tape attached to one point on the edge of
the mirror to put a bit of pressure on the figure by applying tension on
the tape and sticking the other end to the mirror mount. You can experiment
using this technique to see the effects in the star test. Report back on
the sensitivity of the figure to different amounts of tension if you see
changes in the figure. Mounting the mirror with a circular bead (sectioned
into 3 arcs) at the 50 - 60% radius of the mirror should give better
results.

Best,
--Mike Spooner

----- Original Message -----
From: "Rick Maillet" 
To: 
Sent: Tuesday, June 03, 2003 9:13 AM Subject: ATM Star test concerns


>
> I did a star test on vega last night,and the result
> are bothering me, so I need some input please.
> First off, i did not have time to leave the scope
> equalize, but it was out in barn so I doubt if it was
> that far off,
> here is what happened.... was out observing and
> decided to try a star test on Vega, my highest power
> being 250x, telescope is a 10" F-6 dob, in focus I see
> 6 spikes, believe this to be defraction from my 3 vane
> spider, does this sound correct, BTW, I get this
> result on only the bright stars.
> now in and out of focus is the concern, either way,
> the defraction image is nickel shaped,mind you there
> was turbulance in the image but the nickel shape was
> apparent.
> I can tell you this,I had noticed this once before but
> never really thought much of it, I had the mirror out
> last week and reinstalled it after drilling holes in
> bottom of mount to allow air in for cooling down..
> the mirror is mounted on three layers of plywood
> laminated together, with 6 blobs of silicone placed
> according to plop,and three blobs inbetween the posts
> and the mirror, the mirror is 7/8" thick.
>
> Has anyone any idea as to why the nickel shaped image,
> wondering what the culprit is.
> words of wisdom from those who know would be
> appreciated.
>
>      Thanks
>
>       Rick
>
> =====
> Keep looking up,You just may see something interesting.
>
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