Funny diagonal

Can one of you experts tell me what the problem is:

I have a diagonal. Under high powers, the out of focus image shows concentric rings but they are distorted into an oval with a slight kidney bean shape.

The in focus star image is more a little line instead of a point. Is the mirror suffering from astigmatism, if so, how can a mirror have astigmatism?

Thanks,
Ivan

The diagonal mirror may be pinched or improperly mounted and this would cause astimatism. A bad mirror in the diagonal would also be a possiblity.

Is this a diagonal mirror being used with a
refractor? What brand is it? That maybe will give
us some clue to the exact problem and fix.
Or is it a diagonal in a Newtonian reflector?