collimating a 150 mak

[nightfisher]

Looks like i may have to do this task on the 150, its giving poor views and it never used to do this, i have had it apart to check all moving parts, nothing appears to be wrong, so this only leaves collimation.....i have seen inside and it seems the 3 small hex head bolts push against the mirror back plate and the 3 larger ones thread into the back plate, this looks like the small ones are lock bolts, and the big ones move the mirror, does this sound right?, i can see problems when nipping up the little lock bolts, i guess they will push collimation back out of square?

[dweller25]

Hi Jules,

The small bolts are push and the large bolts are pull.

You have to adjust two at a time to collimate ie slacken large one tighten small one. You also have to make sure the bolts opposite what you have changed remain tight too.

When looking through the eyepiece you need to move the collimation in the direction of the thin side of the defocussed star.

Start off by looking down the tube indoors and getting the rings roughly concentric when standing 1.8mts away.

Then start at x200 on a star, defocus to about 5 rings and refine the collimation, improve focus to two rings and refine the collimation, then get accurate focus and refine the collimation again.

Then go to x300 and repeat the above until the infocus star shows a perfectly symmetrical result - job done - good luck

PS - seeing has been very poor recently - so your scope may be OK.....

[gary777]

Looks like i may have to do this task on the 150, its giving poor views and it never used to do this, i have had it apart to check all moving parts, nothing appears to be wrong, so this only leaves collimation.....i have seen inside and it seems the 3 small hex head bolts push against the mirror back plate and the 3 larger ones thread into the back plate, this looks like the small ones are lock bolts, and the big ones move the mirror, does this sound right?, i can see problems when nipping up the little lock bolts, i guess they will push collimation back out of square?

Just to be sure, you did remove diagonal and do some straight veiwing and got the same reslut with different eyepieces...

[nightfisher]

Thanks for the replies, next job is to star test the old girl and see what is what with it, it could be down to poor seeing but i have my doubts

[Avocette]

Having taken it apart to check everything was working was there any risk that you rotated the meniscus lens when you refitted it (compared with the primary mirror) ? This is a problem that Dion Heap once sorted out at an IAS a few years ago.

[nightfisher]

none at all, i always tape mark optics with reference points if they are being taken apart, but good suggestion, however the problem seems to have developed since i removed the corrector to clean it, but i remember putting a piece of tape on the tube, and on the corrector housing

[Avocette]

Have you looked in the 'front' of the scope from the focal length away as mentioned by David (dweller25)? In my case, it was quite clear that there was something wrong in the set up. I have a series of photos I took using my DSLR with telephoto lens set up stably on a tripod at this reference point as I gradually adjusted the collimation screws until the internal ring reflections became more and more concentric. I posted some of them here: http://www.astronomyshed.co.uk/forum/viewtopic.php?f=34&t=21825

[nightfisher]

Not had a look at the front of the scope yet, well saying that shane had a look and thought it was not concentric so i will be doing this first, i am familiar with this mmethod, i used to use this for doing my old omc140 

[Stu]

Not had a look at the front of the scope yet, well saying that shane had a look and thought it was not concentric so i will be doing this first, i am familiar with this mmethod, i used to use this for doing my old omc140

That's a good method to use Jules. This showed clearly that my Mak was out. The primary was not able to be collimated, but it turns out it had come unseated and just needed to be put back in place and the locking ring tightened. Totally different method but similar principle to yours

I assume the secondary is not adjustable?

[spaceboy]

If I remember correctly (half the time I don't  )  you can check collimation on a MAK using a collimator for refractors.

[Skyline]

Maybe this will help...

http://www.telescope.com/assets/product_files/instructions/29291_02-09.pdf

[nightfisher]

Guys, some really good replies posted, many thanks for some top tips, will do the daytime checks saturday morning then see about star testing

[recceranger]

Mate,

I had a 180 and tried to collimated it after ready various guides etc.

A complete frightmare on Elm St! I was chasing my tail and eventually sent it of to a company that supposedly specialised in scope collimation. They didnt!

End result, I sold it and was £128 quid out of pocket due to being taken on by chancers that hadn't a clue.

My advise is bring it to a member that is all over it or get it to astronomia at Surrey Astronomy. They can professionally collimated for around £30 - 40