Quick question on collimating screws..

[bus_ter]

Over recent nights I've been trying collimate my SCT.

Should the screws be tightened down at all? They're currently quite loose and easily turn in any direction. (I assume that's how it should be?)

Also if you tighten one screw say half a turn, must you then unscrew an opposite screw by the same amount? I was collimating the other night and made a number of positive turns, however I didn't loosen off any screws?

[msh1]

this should help you

[bus_ter]

Thanks for the link, that covers the basics well.

I am however unsure about screw tightness.

1) If I tighten one screw, should I unscrew the others?

2) If one screw feels noticeably tighter than the others, should I back it off, tighten the other two until an equal tightness and start over?

3) How tight should the screws be? If they're 'loose' won't the mirror easily move knocking out the collimation? As opposed to tightening down the screws and 'locking' the mirror in place?

[msh1]

ah now your asking something, im not sure, i would ask at a shop or astro club see if they can advise i would have thought they should be roughly the same tight ness like i said not sure hope someone can help you

[bus_ter]

I was able to answer my question in part from some info from the Bobs knobs site (these are thumb screws that replace the regular screws)

I'll paste it here for future searches..

How tight should the knobs be?

After adjusting collimation, the knobs should be neither "too tight" nor "too loose." There is often less than one knob turn between these two extremes, especially on smaller telescopes. (However, see our note below for the Meade six-screw secondary.)

A knob is too tight when there's a marked increase in effort to turn it. Also, the extra tension on the secondary mirror mounting plate may cause optical aberrations to appear temporarily. Forcing a knob even tighter may damage either the knob or the secondary mirror assembly. A knob is too loose when the secondary mirror assembly rattles when a knob is wiggled. A telescope will not hold its collimation when the knobs are loose.

After installing Bob's Knobs, you can easily determine the range between "too tight" and "too loose" by experimenting with them prior to performing the coarse collimation. If you grasp a knob with the same force you would use to pick up a grape, you won't be able to tighten the knob too much -- it will slip in your fingers first. Once all three knobs have the correct tension, collimation is achieved by tightening and loosening different knobs while keeping all three within the correct tension range.

The Meade six-screw secondary behaves differently from the above examples due to the coil springs surrounding each collimation screw. If our installation instructions are carefully followed, the secondary springs will be fully compressed and the knobs will be too tight after installation. Each knob should be loosened one or two full turns before performing rough collimation. This will put the adjustment near its mid-range position. The secondary mirror assembly will not rattle if a knob is too loose; instead, the knob will come completely out of the secondary. To prevent this, do not loosen any knob more than three turns from its fully tightened position. More information on the Meade six-screw secondary can be found here.