Quote Originally Posted by narsuitus View Post
I do, however, notice image degradation caused by mirror vibration when I mount my camera on a telescope and use a shutter speed between 1/2 second and 1/15th second. Thank goodness my SLR's mirror lock-up feature is very useful for avoiding this degradation.
I would submit that the focal length of a telescope is much longer than camera lenses [ignoring mirror lenses] and therefore 1/[focal length] << 1/2 second or 1/15 seconds.

Steve