Sct collimation

[DavieH]

Hi, I have an Evolution 8 that needs collimation - I'm sure there must be a thread somewhere on SGL with a tutorial, but I can't find it. It's the first time I will have done anything like this so ideally idiot proof and words of one syllable of possible!

[SthBohemia]

22 minutes ago, DavieH said:

needs collimation

Embark on an internet search- "How to collimate an SCT". You will get a myriad of methods, simply be aware that the laser collimators that claim to make matters simplistic are notoriously INACCURATE and need collimating before being relied upon to collimate a SCT...

[Mr Spock]

17 minutes ago, SthBohemia said:

be aware that the laser collimators that claim to make matters simplistic are notoriously INACCURATE and need collimating before being relied upon to collimate a SCT...

Or be aware laser collimators don't work on SCTs 

Best method I found was a two step process.

Step One: In daylight. Place the SCT so you can look down the tube from about 2-3 metres away until you can see the tube, mirror and secondary. Adjust the collimation screws until all the circles you see are concentric.
Step Two: Star test. Have an eyepiece which gives around x200-x300 with a 2nd mag star central defocus until you have a series of circles with a bright dot in the centre. Adjust the collimation screws until all the rings are concentric while all the time keeping the star in the centre of view.

[SthBohemia]

10 minutes ago, Mr Spock said:

Step Two: Star test. Have an eyepiece which gives around x200-x300 with a 2nd mag star central defocus until you have a series of circles with a bright dot in the centre. Adjust the collimation screws until all the rings are concentric while all the time keeping the star in the centre of view.

^^ rely on that one and forget any other methods an yas' canna go wrong :-)....

[DavieH]

Thanks all - if it ever stops raining i will give the two steps a go Mr Spock!

[Elp]

Though it doesn't address the orientation of the corrector plate which "usually" doesn't need adjusting from the factory setting (it's easy to check this if you align a camera to the centre axis a few metres away from the SCT aligned horizontal to the ground so the camera looks directly down the tube, you can see how concentric everything is in relation to each other), for the secondary use a Duncan mask:

http://alpha-lyrae.co.uk/2013/12/31/schmitt-cassegrain-collimation-made-easy-using-a-duncan-mask/

[DavieH]

Thanks for the link Elp