What is Mirror Lock-up?
A. Mirror lock-up is the ability to flip up the mirror and hold it there independent of releasing the shutter. This prevents any vibration resulting from the mirror action affecting the sharpness of the picture. This is achieved on the F4 by moving the lever on the body made for this purpose. The mirror swings up and stays there until you move the lever back. Obviously, the camera must be mounted on a tripod and the picture composed before the mirror is locked up; otherwise you do not know what you are shooting, exactly. The value of mirror lock-up is debated; most people think it is not helpful at fast shutter speeds because the mirror action is over and the picture made before any vibrations would shake the body and affect picture sharpness. The value of mirror lock-up is most seen at slower shutter speeds in the 1/15th to 1/2 second range, where many pictures are taken with slow, fine-grained film. Some bodies have a simulated mirror lock-up in that one can set the timer, which will
