Collimation

[Herzy]

I have a C6-N and there was a metal plate at the back of the telescope that I took off to reveal the Collimation screws. There are 3 big silver screws and 3 small black screws. Which ones do what?

[Starwiz]

I don't know the scope, but one set of screws (usually the larger) will be for adjusting the mirror position and the other for locking the mirror position during collimation.

John

[brantuk]

If you look inside the rim at the screws - the three with a spring round them are the collimating screws - the others are the locking ones. Loosen the lock screws so you can adjust the sprung ones to collimate. But you do need a collimation tool to do it right. So I wouldn't touch it unless you're sure of what you are doing - if you misalign it then it could take weeks before you have it back properly.

Best thing is to pop along to a local astro club meeting and ask a colleague for help doing first time collimation.

[Herzy]

Well let me give you a run-down of what I'm going to do and you can point out any errors.

1) I'm going to put in my laser collimate and adjust the secondary mirror screws untill the laser is in the exact center of the primary mirror.

2) I'm going to slightly unscrew the locking screws and adjust the larger screws untill the laser is in the center of the laser collimator target.

[brantuk]

Ahh - you seem to have a good idea about it all. So if you identified the colli screws I'd say you're good to go. Just don't do the lock screws up too tight once you're finished - just snick them up to meet the mirror cage without overdoing the pressure on it, or you risk knocking collimation off kilter again undoing all your good work. Good luck!

[Herzy]

Thanks, one final question. Does the secondary mirror have a lock screw? There is a big screw in the middle, is that it?

[brantuk]

Yup the one in the middle is the secondary lock screw - only slightly loosen it though enough so the other screws will tilt the sec mirror. And keep track of how many time you loosen it to collimate - don't want the secondary mirror dropping out and falling on the primary.

[Dave In Vermont]

Brantuk's advice is quite right. I'd also suggest you perform the collimation of the secondary with the scope either level, or pointing a bit downward in the front. This is for when (not if) you manage to drop your wrench!

A little fun everybody manages to do once or more.....

Dave

[rockystar]

first thing I did was invest in some Bob's Knobs collimation screws, for the primary and secondary; that way, no tools required, so zero chance of dropping your wrench on the primary

however, make sure you have some idea of what you are doing first, as it will be *way* out after you have changed them.

from memory, I think the grub screws are the locking ones and the driver required screws are the collimation screws.

[opticalpath]

I'd suggest you do any secondary tilt adjustment using only the three adjustment screws and not touching the central screw. It's not so much a 'locking' screw, but rather a retaining screw.  Make the adjustments in very small steps.  Start by loosening one of the three by a small amount and immediately take up the slack by tightening one or both of the other two.  If you do it this way, always balancing loosening of one with tightening of another, everything should remain snug without the need to touch the central screw.

Adrian