Re: [ATM] Ghost image

[Jarvis Krumbein <jkoptic@juno.com>]

I had a similar Coulter Blue Tube a number of years ago and found that
the adhesive that was used to hold the secondary in place was much too
hard and thin.  This resulted in astigmatism which was quite bad. 
Removing the secondary and re gluing it in place using silicon adhesive
cured the problem.  I've seen problems like you describe when a thin
secondary was hard glued to its support.  Have you checked this?  I doubt
that the primary mirror is the problem.

Jarvis Krumbein

On Thu, 19 Apr 2007 11:58:24 -0700 (PDT) vorblesnak@peak.org writes:
> It has been busy, so although I have read your suggestions I have not 
> had
> a chance to test them all.  I have done some ..
> 
> I rechecked the collimation, including rotating the laser collimator 
> in
> the focuser tube.  There is a bit of slop in the tube.  The return 
> dot
> from the laser almost goes off the hole of the laser collimator, but 
> never
> completely.  So there is a bit of wobble.  It is a home made laser
> collimator.
> 
> It is a sealed tube so the mirror does cool very slowly.  It has 
> been
> stormy here so I have not had it out long enough to allow the mirror 
> to
> cool in the tube.  I like the idea of opening the trap door to allow 
> the
> mirror to cool prior to viewing.
> 
> I rechecked the figure of the primary, it looks good to me.  Using 
> Windows
> Ronchi the figure looks the same as the example in the Ronchi 
> program.  I
> do not have a foucalt tester.
> 
> There is no pinching in the primary cell that I can see.  The mirror 
> sits
> on a strap that is supported above the diameter of the mirror, but 
> flares
> away from the mirror below the diameter. (does that make sense?)  
> There
> are stops on the posts that hold the primary to keep the mirror 
> from
> tipping out, they do not touch the mirror.  The back of the mirror 
> is
> irregular but there are only three contact points and it does not 
> look
> like they touch any of the surface defects. The mirror is about 
> 1.25
> inches thick.  It is very white glass, not indication that it is 
> Pyrex or
> not.
> 
> The coating on the secondary is good.  Both mirrors are dusty but 
> not
> overtly dirty.
> 
> I adjusted the primay mirror in it's cell and tried another view.  
> I
> looked at Saturn again.  After all of the above fiddling, and a 
> couple of
> days waitting for a sucker hole, the 'blob' was now on Saturn as 
> opposed
> to being next to it.  It appears to be the same size.  I was not able 
> to
> move around the eyepiece and find a spot where the 'blob' 
> disappeared. 
> Stars and deep sky objects do not show the blob, or it is so 
> diminished
> that I cannot see it.
> 
> When I get a clear night and some time I will try the other 
> suggestions. 
> And yes, if I can I will take an afocal picture.
> 
> 
> David Davis
> Toledo, OR 97391
> 
> 
> 
> 
> 
> 
> 
> 
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> 
> 
 
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