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How to collimate 400mm classical cassegrain

Collimation

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#1 nakbrooks

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Posted 12 November 2013 - 04:21 PM

I'm attempting to adjust collimation on my 400mm classical cassegrain for the first time.  I have the ASA laser collimator and I've read the collimation manual (http://www.astrosyst...on_Manual_E.pdf).  However this lacks information on the physical location and operation of the collimation screws.

 

Specifically, there are 9 screws on the back of the primary mirror cell:

 

  -  I understand that some are "push" and some are "pull", but which are which?

  -  Do they rotate clockwise or anticlockwise?

  -  How tight should they be adjusted to prevent movement but avoid damage?

  -  What is the recommended procedure (adjust one set of 3 while keeping the others tight, loosen all "pull" screws first then adjust, or what)?

  -  What is the recommended attitude when collimating (e.g. OTA pointing at zenith so primary rests evenly on "push" screws)?

 

Similarly there are screws both on the back of the secondary mirror cell and the side:

 

  -  Which of these are used for collimation adjustment, and how?

 

May be obvious questions, but I don't want to risk damaging the mirrors or making collimation worse (it is currently only slightly out) so am looking for detailed guidance (ideally with photos so it is absolutely clear which screws are which) before I attempt this.

 

Many thanks

 

Nigel


Edited by nakbrooks, 12 November 2013 - 04:22 PM.

Nigel Brooks
Stratis Observatory, Hautes Pyrénées, France.
http://www.facebook.com/stratisobservatory

#2 MarkS

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Posted 19 November 2013 - 07:46 AM

Hi Nigel,

 

Since no-one has offered any suggestions, have a look at the manuals for the N series Astrographs. There they identify the pull and push screws. The pull screw is the middle one in each group of three, flanked by a push screw on each side. 

 

And there is a bit about collimation, though the English language instructions are not all that clear. Whether this is relevant, I have no way of knowing.

 

Your description matches what my N10 looks like. Your main cell may well be similar in basic construction - except the mirror won't be glued to the frame, I guess.

 

Hope this might help a little!

 

Regards,

Mark



#3 nakbrooks

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Posted 19 November 2013 - 09:22 AM

Thanks for that Mark. Yes, the N series manuals help a bit, although the physical details of the Cassegrain cells are somewhat different.

ASA have promised a more detailed collimation manual for the Cassegrain OTAs, hopefully in the next few days.

At present I'm waiting for a forecast of 3 consecutive fairly clear nights before I fly down to the observatory (in the Pyrenees) to polar align, collimate and achieve first light. Looking at the forecasts now that could be a long wait :(

Nigel
Nigel Brooks
Stratis Observatory, Hautes Pyrénées, France.
http://www.facebook.com/stratisobservatory





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