SCT Collimation

[JayStar]

I am currently getting rather obsessed with collimation of my SCT (CPC925).  

Having removed the secondary mirror - accidentally (dont ask!) - I had the task of getting things back in line and followed the instructions for de-focusing a star and trying to ensure that the diffraction pattern was correct.  Did that and I think got it was close but I was also wondering if there is a way of getting close to proper alignment of the primary and secondary mirrors during the day by just looking down the optical tube.

 I did this today and noticed that when looking down the optical tube from behind the primary (with no visual back or eyepiece) you can actually see the secondary and the housing and if you look  dead on and then move your head slightly side to side and up and down you can spot if it is not quite aligned.  Is this an ok thing to do to get a rough collimation done before that star test?  Are there any other ways of collimating during the day?

[Uplooker]

Can't help with collimation during the day but try using  Als Collimation Aid which can be found here:-

http://www.iceinspace.com.au/forum/showpost.php?p=589542&postcount=47

[Laurie61]

I usually look in the front as a quick check, stand about 3-4 m away and move your head around optical axis, as you have been doing. If it looks close then star test when dark. I have found that always moving the focus knob the same way to focus, (clockwise for me) for collimation and general viewing helps remove any mirror flop effects.    

[Peter Drew]

Looking down the front or back without an eyepiece to check concentricity usually gets the collimation near enough for a star test. Moving the primary in the  direction in which the final collimation was performed is important as mentioned by Laurie61.  

[Gazabone]

Personally I find the Hotech collimation tool very good. If you're into gadgets you'll love it as well as enabling you to collimate during daylight in quite a confined space. The secret is to take your time setting it up and making sure you do that accurately, actually adjusting the scope is the work of s couple of minutes after that. Works on cats 7" and up.

http://www.firstlightoptics.com/hotech-collimation-tools/hotech-advanced-ct-laser-collimator.html

[JayStar]

I got the hubble articial star - very cheap - and it works perfectly.  I can place the star about 12 metres away in the garden and get the out of focus position I need to collimate.  Use the DSLR live view to do it and its easy - with the grid view on the live screen positioning the artificial star dead centre is simple.

[astroalex]

As JayStar says, artificial star is probably the best bet during the day. Looking down the barrel is very rough collimation only. Unfortunately my garden is too short to focus my C11 on an artificial star.

This write up by Thierry Legault about collimation is the best I managed to find http://www.astrophoto.fr/collim.html.

Also, I highly recommend Bob Knobs thumb screws, for me they made a tremendous difference. I do not quite understand why Celestron does not ship it by default. But make sure you carefully follow installation instructions and do not drop your secondary mirror.

[anthony]

I found this link particularly good for mine

http://www.astromart.com/articles/article.asp?article_id=548