150/750 collimation

[Andy78]

hi all... ive managed to pick up what looks a TS 150/750 on a eq3 mount for £30, bargain i thought. But when i checked the collimation i noticed that when looking through the focus tube you cant see any of the primary mirror clips, looks like the secondary is too small. ive got the secondary centred under the focuser but no joy. and the primary hasnt got a centre spot but im going to clean the primary at the weekend and sort that out then. can anyone offer advise on how to collimate it???

[NGC 1502]

Is the focuser racked far enough inwards ?

If its too far out, then the primary mirror clips may not be visible.

Worth checking before looking further.

Regards, Ed.

Edit - link here showing size of secondary with 6" mirrors http://www.image-optics.fsnet.co.uk/telescope4.htm (scroll down)

[Andy78]

im sure I checked it like that aswell as all the way out. im at woprk at the moment but wii double check when I get home. thanks.

[Astro_Baby]

Are you using a cheshire for this ? Some scopes might nit show the clips with a cheshire collimator depending on the cheshire. A collmation cap might help or a very short barrelled cheshire...either might show the clips. If not you can always resort ro the mark one eyeball.

[Andy78]

Im just using a collimation cap at the moment and the misses has got me a laser for xmas (i broke my last one... dropped it) but still no primary clips unless i tilt the secondary over too much and then its not centered under the focuser and doing that only shows one clip depending on the way its twisted. Theres a video on you tube of an Omegon 150/750 collimation but its in french. Itsvthe exact same as the scope ive got and you cant see the clips on that either when it show you a shot down the focuser. If it cant be done? Then at least i got an eq3 for £30. Still a bargain!!!

[Astro_Baby]

Hmmm sounds like the secondary might be a teensy bit undersized. The problem with a laser is it can be very misleading with regard to secondary collimation.  You can make a laser hit the centre spot and get a reflection even if the secondary is twisted.

[Andy78]

Thanks for the info. I will get a short tube cheshire in the new year. I too think that the secondary is a bit small but even in its present condition it gives good views though. So if i were to sort out out issues and sell it on. I could get a neat little profit to put towards other scope stuff.