Pinched mirror

I was wondering if some one could clear something up for me.
If when focusing a DOB and it is out of focus, you see ghost images that merge (or nearly) when focused, does this mean the mirror is pinched. I have seen this in one DOB and the mirror is held tightly in the mirror cell, no play in mirror at all. The mirror is tight becuase the 3 clip posts that hold the mirror actually touch the sides of the mirror not because it is glued in place. There are 3 ghost images, so I figured that this was the likely problem.
I would like to find the source of this aberation and correct it. Any suggestions would be appreciated.
Thanks,
Floyd

Floyd, not sure I full understand what you are describing but it could be a pinched mirror. How thick and what diameter is the mirror?
I had an 8" f/6 that was glued to a plywood mirror cell with silicon rtv. It had performed flawlessly for over a year then one night the star images looked like "-".
Just a line. I took the mirror off the cell and remounted with clips and rubber pads. Back to normal.
You could easily lighten up on the clip pressure and should be able to see immediately if that helped.

Walt

Dan,
What you are describing is very much what I am seeing in this DOB. There are 3 ghost images when the object is not in focus, plus the actual main image. These 3 ghost images begin to merge with the real image but do not merge completely when it is fully focused. This only is visable with a large bright object like Mars. Stars look normal and so do DSOs. The view is very acceptable except when I try to view Mars at this time. I have not used this scope for planetary before, so I have to assume it would be the same with any other bright large object.

I am not sure what was used to attach the secondary. I will have to try to find out what.

I had not really thought about the secondary mounting, though I had considered the problem to be related to the secondary and not the primary.

I had thought that the fact that the primary was being held too tightly by the posts, not the clips, might be the problem. The posts are supposed to support the mirror, but have a small gap between the mirror and the cell clip posts. The padding on the clip posts was too thick allowing no gap between it and the mirror. This was fairly tight! Now I have made a gap and the mirror is free floating on the cell. The gap is very small, but enough to allow the mirror to be moved ever so slightly side to side.

The secondary has been mounted for over a year, but it is a definate possibility. I will have to look into that more thoroughly. Was you secondary mounted to a plate directly by adhesive or is there a pad of material between the plate and the mirror?
Thanks for all your responses,
Floyd

Floyd, what do star images look like out of focus? Start with a brightish star in focus, then slowly defocus. If the star image expands into a circular or nearly circular disk, then the primary is probably not pinched. If it is pinched, then the out of focus star image will have some kind of peculiar outline, like triangular (in a cell with three too-tight clips like you described), or some other irregular outline.

Doug Scobel