Yes it does. It is on the laser carriage which is mounted to the the long screw drive under the top cover. I wouldn't mess with it unless you know what you are doing. In my experience, unless the the mirror is incredibly dirty you won't see much change in image quality. A dirty mirror wouldn't effect plate longevity. It can effect screen quality but only if you are running very fine screens generally 150 lpi+. That is assuming that you are outputting at 2400 dpi or higher. Have you checked your screen calibration? Also what type of plate are you using and how long have you been dealing with this issue?