Primary Mirror Shifting

[NickRose2006]

I need some suggestions with my primary mirror. I have a Vixen/Celestron SP-C6 Newtonian and have noticed that the primary mirror shifts, not by a whole lot but to me any shift is bad. Should I tighten the mirror clips more or do something else, like put bumpers on the side part of the mirrors. I guess I can tighten the clips a bit more but not much since that could damage the mirror.

[John]

The mirror clips should not be tight - the classic advice is that you should be able to get a piece of thin card between the clips and the mirror - but don't try it - it's just illustrating that the clips should not be tight onto the mirror surface to avoid distorting the mirror.

If the mirror is moving from side to side in the cell then some packing might help, but there again not too tight.

Some manufacturers use double sided sticky pads on the bottom of the mirror to hold the mirror in place in it's cell.

[NickRose2006]

Yeah I wont touch the clips, they're already at the point that you described. The mirror does have one of the sticky pads but maybe it should be replaced. It has been there for maybe close to 30 yrs.