Mirror lock-up
Encyclopedia
Single-lens reflex camera
A single-lens reflex camera is a camera that typically uses a semi-automatic moving mirror system that permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to pre-SLR cameras where the view through the viewfinder could be significantly...
(SLR) cameras. It allows the operator to reduce vibration
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
-induced motion blur
Motion blur
Motion blur is the apparent streaking of rapidly moving objects in a still image or a sequence of images such as a movie or animation. It results when the image being recorded changes during the recording of a single frame, either due to rapid movement or long exposure.- Photography :When a camera...
during exposure
Exposure (photography)
In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...
. It also allows the mounting of lenses which extend into the SLR's mirror box when mounted.
Reducing vibration
Normal operation in an SLR cameraCamera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
involves flipping the mirror up out of the light-path just before the shutter
Shutter (photography)
In photography, a shutter is a device that allows light to pass for a determined period of time, for the purpose of exposing photographic film or a light-sensitive electronic sensor to light to capture a permanent image of a scene...
opens, and then returning it when the shutter closes (although very early SLR's required the shutter to be cocked for the mirror to return). This causes vibration of the camera, particularly when the mirror slaps into the top of the mirror box. This vibration quickly dies away so the most motion blur is actually seen with short shutter times that capture multiple 'swings' of the vibration
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
. While longer exposures will capture all of the vibration
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
s, the exposure will be dominated by light captured when the camera is vibration-free (assuming a steady mount).
Mirror lock-up involves flipping the mirror up well before the shutter opens, allowing the vibrations to die down before exposing the film. On some cameras MLU may be operated by an extra push of the shutter button, the second push resulting in the actual opening of the shutter. Other arrangements may involve an extra lever or button that flips the mirror up before using the shutter release button normally. On some cameras MLU is not a separate feature, but operated as part of the self timer
Self timer
A self timer is a device on a camera that gives a delay between pressing the shutter release and the shutter's firing. It is most commonly used to let photographers to take a photo of themselves , hence the name....
.
Note that when the mirror is in the up and locked position, the subject is no longer visible through the viewfinder
Viewfinder
In photography, a viewfinder is what the photographer looks through to compose, and in many cases to focus, the picture. Most viewfinders are separate, and suffer parallax, while the single-lens reflex camera lets the viewfinder use the main optical system. Viewfinders are used in many cameras of...
. Therefore, the photographer must compose the photograph prior to activating mirror lock-up and keep the camera from moving. Use of a tripod
Tripod (photography)
In photography, a tripod is used to stabilize and elevate a camera, or to support flashes or other photographic equipment. All photographic tripods have three legs and a mounting head to couple with a camera...
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.
Lenses requiring mirror lock-up
Some lenses are designed such that they extend into the mirror box when properly mounted on an SLR. These may include early wide-angle lenses for SLR's, certain lenses designed for rangefinder cameraRangefinder camera
A rangefinder camera is a camera fitted with a rangefinder: a range-finding focusing mechanism allowing the photographer to measure the subject distance and take photographs that are in sharp focus...
s, and certain other non-SLR lenses adapted for SLR use. Mirror lock-up must be activated prior to mounting such lenses, and kept in place in order to prevent damage to the lens and/or camera. This method of operation prevents any use of the SLR viewfinder with the lens. Prior to the development of lenses utilizing the Angénieux retrofocus
Angenieux retrofocus
The Angénieux retrofocus photographic lens is a wide-angle lens design that uses an inverted telephoto configuration. The popularity of this lens design made the name retrofocus synonymous with this type of lens...
concept, mirror lock-up was essential to wide-angle SLR photography.
External links
- Understanding Mirror Lock-Up on The Luminous Landscape
- Mirror Lock Up by Bob Atkins on Photo.net