A Secondary Rotation Error Question

[pat]

I've taken apart my reflecting scope to clean it. I used AstroBaby's collimation guide. How can I knew if the secondary is correctly rotated? Without a hit and miss eyeballing it or useing a star test. I have a Cheshire(no x-hairs)and no laser. I've heard of a German device that solves this problem. Is there a foolproff way to insure that the secondary is correctly turned? Thanks, Pat

[Moonshane]

basically if the silvered surface presents a round shape to the eye then it's turned correctly. take everything out of the focuser, take off the cap and then looking down the focuser from maybe 6" you'll see if it's round or not. this only addresses the turning aspect. you need to make sure it's central too but that's another step in the process.

if your 'spy hole' in the Cheshire is large enough then you may be able to check both of the above with that. I find that with my Cheshire there's not enough view to see the whole secondary on some of my scopes, this being worse for faster scopes with a bigger secondary.

[cantharis]

Thanks moonshane - I was wondering about that one.

[cosmojaydee]

If you pay a visit to Astronomy shed , there is a complete guide to rebuild including collimation from focuser to secondary to primary all three are important to a complete rebuild . Collimation starts at the focuser , if this is not set nothing else will fall inline

[Moonshane]

although I do agree that technically the focuser should be square to the OTA, there is capacity for adjustment of all the components so it's not something to overly worry about, especially for visual. generally, if it looks good then it probably is good.