Re: [APML] Help! Advice on collimating a C14

[Duncan Munro <dmunro@sfu.ca>]

Andrew,  I have collimated lots of SCTs and in my experience they do not 
lose their collimation easily if collimated properly, and they are easy 
to collimate unless something is wrong. You should start by tightening 
down (firm but not too tight...)all the collimation screws and then 
starting the collimation process again. This time you will back the 
screws off as you collimate so that when you are finished the screws 
will still be reasonably tight. I'm not really a fan of bobs knobs 
because I rarely have to recollimate and I find the allan keys allow for 
finer rotation of the screws.

Does your C-14 have the removeable secondary? It's possible that 
something is loose which is allowing the secondary assembly to move 
around. Also check the corrector plate screws and see if they are all 
snug. I used a Meade 16" SCT extensively and the corrector plate had a 
tendency to move around. IIRC we put some extra spacers around it to 
hold it in place.

When you  observe a star at high power are you seeing concentric 
diffraction rings?

t will probably take a C-14 a couple of hours to cool down. Planetary 
viewing will suffer greatly until the tube currents start to go away. 
Tube currents can mimick rough optics and/or poor collimation.

cheers

Duncan

Andrew Clegg wrote:

>Gang,
>
>This may not be the best place to ask this question, since everyone seems to
>use RCs or refractors, but I thought I'd ask anyway...
>
>I have a C14 CGE, and I am having one &$%#^ of a time getting the thing
>collimated. Deep sky views are spectacular, but lunar and planetary views
>are basically horrible (my Orion ED80 gives better views). This is
>frustrating because in the reviews of the C14 CGE that I've read, they often
>mention that the 'scope provides some of the best lunar and planetary images
>the reviewers have ever seen.
>
>As I eventually want to move past piggyback astrophotos to shooting through
>the C14 itself, I need to find a way to get good collimation. I've tried
>collimating on stars (with the help of a friend), but the process is very
>slow, tedious, and frustrating (even with Bob's Knobs), and never ends up
>with greatly improved images. And when the 'scope is packed up for the
>night, collimation is lost, and the next observing session is once again
>spent mostly on collimation, in a vein attempt to improve the images. Arghh.
>
>I've read almost everything I can on the tricks of star collimation, but it
>just ain't working for me. So the next option is one of the specialized
>laser collimators for SCTs, which shine through the optical path of the SCT
>in reverse and project a scattered laser spot onto a distant target. I
>wouldn't mind trying that, but I really would like to know if anyone has any
>experience collimating SCTs (either with a laser or something else) before I
>shell out $200 for the laser collimator. Another choice would be collimating
>on an artificial star, but again, it would be good to hear some opinions
>before sitting down at the workbench to make one of these.
>
>Has anyone had the same trouble as me getting a large SCT collimated? Should
>I send the OTA back to Celestron to make sure there isn't something wrong
>with the optics? That would cost me a couple hundred bucks, but it would be
>worth it if that would cure my problems.
>
>Help!
>
>Clear skies,
>Andy
>www.w4je.com
>
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>
>  
>

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