Mirror lock-up
From Wikipedia, the free encyclopedia
Mirror lock-up (often abbreivated to MLU) is a technology employed in many SLR (Single Lens Reflex) cameras today to reduce vibration when taking photographs, especially at longer (slower) shutter speeds.
With mirror lock-up in use, the camera requires an extra push of the shutter release button. The first push flips the mirror up and away from the film or sensor. The camera then adjusts to the correct F stop. The photographer then pushes the shutter release for a second time. This then opens the shutter and exposes the film or sensor for a predetermined time. The shutter closes, the aperture reverts to it's wide open setting and the mirror flips back down.
Note that when the mirror is in the up and locked position, one can no longer see the subject through the viewfinder. Therefore, the photographer must compose his photograph prior to mirror lock-up and keep the camera from moving. Use of a tripod helps prevent movement of the camera during this operation.
Combined with a remote or cable release, this greatly reduces the potential for vibration of the camera.
