Is my mirror tight enough?

[Lee]

How tight is too tight for the rubber clips on a newtonian primary? I've just found out.... image attached.
I cleaned my mirror 2 weeks ago, and was very careful to not tighten the clips much then.... round stars, but possibly more differential flexure (I think?). So I decided they might need a little tightening.... now I have triangle stars! :mad2:

[h0ughy]

yep too loose then too tight - there must be a just right position

[Allan]

When I bought my scope I checked how the mirror clips had been tightened from the factory. Interestingly, one screw on each clip was quite tight and the other very loose, so that the rubber clips were bearing down on the mirror at an angle.

A lot of the information I found stated that the clips should not touch the mirror, but just sit a fraction of a mm above it to prevent it from falling out of the mirror cell.

I hope that is correct, because that is how I've set my mirror clips.

[asimov]

That's the correct info, Allan.

[astro_nutt]

An easy way is to place a piece of paper between the top of the metal plate sitting on top of the rubber clip and under the head of the screw. Tighten the screw until it touches the paper. That should be sufficient.

[Lee]

I loosened it up yesterday, rubber was ever so slightly missing the glass, didn't allow you to lift the mirror, but allowed you to rotate it.... round stars again! :)

[bojan]

Of course!
Mirror was manufactured and tested without any clips...