Collimation having a nightmare help needed

[Steve Wright]

I have an old Astrosystems 10" reflector, I made the mistake of taking out the mirror cell to clean it and ever since I have not been able to get the collimation right.

I have a laser collimator which I have made a bench V frame for so that the Collimator itself could be checked and collimated, the trouble I seem to have is that there is sufficiant movement in the focuser tube to alter the return beam of the collimator and I am unable to decide when collimation is spot on.

Any suggestions would be greatly appreicated as I am not able to use the scope at the moment and am restricted to my portable Maksutov

[Merlin66]

Forget the laser.....

Just use a collimation cap - get everything as concentric as you can and enjoy using the scope!!

That will certainly get you close enough....you can then judge if you need to do any more by looking at the slightly out of focus image of a star....adjust the secondary very gently to centre the doughnut.

[damnut]

Have a quick search through youtube, there will be a vid on there also. Took my newt when I had it to Rother Vally Optics, they charged a tenner to properly collimate it. I then marked all the screws. Able to keep in collimation using an empty film tube with drillled centre hole..

So you may find a local astro shop that will do it cheaply, it was a tenner well spent after all the time I had spent putting it out of alignment!

Good Luck

[Steve Wright]

Hi Merlin66,

Thanks for your reply, I have heard of using a 35mm film pot with a hole drilled in it, is this the method?

The trouble is I am not sure what size hole or how to tell when everything is concentric, do you have to be able to see the primary mirror clips around the edge and what position is it best to have the focuser in, right in or right out, does that make a difference?

Been frustrating me for ages this issue, thought I had it spot on and Jupiter looked like an egg even 'in focus', I am beginning to think there is something wrong with my eyes now that I am approaching my 50th year...lol!

[Essex Stargazer]

Sounds like you may need to upgrade the focuser , movement is not good news

or do as the other 2 poster have suggested

Hope you get it sorted soon

[John]

One of our members, Peter Drew, knows a lot about those scopes and may be able to provide some help. I used to have the 6" version and it's primary mirror did not have any collimation adjustment - collimation adjustments were made using the 2-vane secondary support with which you could rotate and tilt the secondary mirror to achieve collimation. Is that the same design your 10" uses ?.

Also, when you removed the mirror cell, did you return it with the mirror orientated the same way it was originally ?. I put alignment marks on my mirror cell and tube to ensure that I did this with mine.

I seem to recall that the primary mirror was not centre spotted with my 6" - that does not make it easy to use a laser collimator !.

I reckon the above advice not to use a laser collimator but to revert to a simple collimation cap is probably sound. Astro Systems supplied a nice machined alloy cap for that purpose with my scope.

[Merlin66]

Yes, the 35mm canister will do the job, a 1.5 -2mm central hole.

Focuser in or out doesn't matter - what ever gives you the best view of the primary mirror edge.

Don't get too hung up about how concentric is concentric...give it your best shot and I can assure that will be good enough to be able to use the scope.

[Peter Drew]

The 10" F4 is naturally more sensitive to collimation than the longer focus versions. I presume that you mean the fit of the laser unit is the problem rather than a loose drawtube. If you have'nt removed the secondary mirror or holder this is probably still correctly positioned. I would use the laser to get the collimation about right and then do the final tweaking on Polaris, IMO star testing for fast optical systems is the definitive final method.

[callisto]

Check the primary mirror clips and make sure they are not over tight, this can nip the mirror and effect collimation

[Steve Wright]

Made a collimation cap and with a little fidlling I think I have it set up much better, first views of Jupiter was good tonight showing four Moons and a little structure, went for the webcam but beaten by the clouds so have packed up now but an encouraging start, thanks for the advise, looking forward to Kelling now.

[umadog]

Hmmm... I feel that at f/4 you're going to need to do better than cheaply made collimation tools. A wobbly laser is no good, obviously. I'd go to the Catseye site and buy the Cheshire (blackcat) and the auto-collimator (XLK). The pair of them are more accurate than a laser although they are slightly less intuitive to use at first.

Star testing shows you that your collimation technique is working but once you've verified that once (and you should) then you don't need to keep verifying it that way. It is easier to achieve accurate collimation with the right tools than it is to do so with a star test.