Mirror lens question

[LightHunter]

Can you inform me about your experience with a 500mm or 600mm mirror lens used with a Canon EOS 10D?

[RichardtheSane]

Used them with film and hated them.

Not very good quality, rather soft to be honest. And some really wierd effects in the out of focus areas.

But on the flipside, if it gets you the shot none of your other lenses would...

[Jesper]

I've never used a mirror lens myself, but one of the not-so-great things about them is that out of focus areas will get the shape of a donut instead of a circle. It looks a bit weird and not nice, here's an example: http://www.kjsl.com/~dave/owls/reflex.html

Here is a description of mirror lenses: http://www.photo.net/learn/optics/mirrors/