- Flange focal distance
The flange focal distance (FFD) (also known as the flange-to-film distance, flange focal depth, flange back distance (FBD), or register, depending on the usage and source) of a
lens mountfor an interchangeable lens camerasystem is one of its most fundamental attributes. This is the distance from the mounting flange—the metal ring on the camera and the rear of the lens—to the film plane. This value is different for different camera systems. The range of this distance which will render an image clearly in focus within all focal lengths is usually measured in hundredths of millimeters and is known as the depth of focus.
This distance influences whether a lens from one system can be mounted with an adaptor to a camera body of another system. In order to produce an adaptor that permits focus to infinity without corrective optics, the flange-to-film distance the lens is designed for must be greater than that of the camera body it is to be adapted to, to give room for the adaptor. Camera systems with a large flange-to-film distance have lenses that can be widely adapted, while those with a small flange-to-film distance can take adaptors for many types of lenses.
If the difference is small, other factors, such as the diameters of the mounting flanges of the two systems, come into play as well. Camera bodies with wider lens mounts are easier to produce lens adaptors for.
Systems with short flange-to-film distances include Canon's FD (42.00 mm) and EF mounts (44.00 mm),
Konica's AR (40.70 mm), and Olympus's Four Thirds System(38.67 mm). These can readily take many other brands of lens.
Systems with larger flange-to-film distances include Nikon's F-mount (46.50 mm), Olympus's OM mount (46.00 mm), and the
Pentax K mount/M42 (45.46 mm) universal thread mount. These lenses can be adapted to many camera bodies.
Micro Four Thirds Systemhas a flange-to-film distance of only 20 mm. This is enabled by the lack of a reflex mirror.
Flange focal distance is one of the most important variables in a camera, as lens seating errors of as little as 0.01 mm will manifest themselves critically on the imaging plane and focus will not match the lens marks. Professional
movie cameras are rigorously tested by rental houses regularly to ensure the distance is properly calibrated. The most common mount is the PL mount with an FFD of 52.00 mm. The Russian OCT-19 has an FFD of 61.00 mm. Any discrepancies between eye focus and measured focus which manifest themselves across a range of distances within a single lens may be collimation error with the lens, but if such discrepancies occur across several lenses, it is more likely to be the flange focal distance or the groundglass (or both) which are mis-set. As per depth of focus, discrepancies should be much easier to spot on wider lenses than on telephoto ones.
Due to research on optimal flange focal distance settings, it is currently considered more optimal for flange focal distance to be set to somewhere "within" the film's emulsion layer, rather than on the surface of it. Therefore, the nominal flange focal depth will be equivalent to the distance to the groundglass, whereas the actual flange focal depth to the aperture plate will in fact be ~0.02 mm less.
List of lens mounts
* Markerink, Willem-Jan. " [http://www.a1internet.nl/phomepag/markerink/mounts.htm Camera Mounts & Registers] ". Retrieved on
November 6, 2005.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Micro Four Thirds system — The Micro Four Thirds system (MFT) is a standard created by Olympus and Panasonic, and announced on August 5, 2008, for mirrorless interchangeable lens digital cameras and camcorders design and development. However, unlike the preceding… … Wikipedia
Canon EF lens mount — The EF lens mount allows all the Canon EF lenses to be used on any of the Canon EOS line of cameras made by Canon Inc.Unlike the EF s breech lock predecessor, the FD mount, the EF mount uses a bayonet style mount. EF stands for Electro Focus :… … Wikipedia
Arri PL — is a lens mount developed by Arri for use with both 16 mm and 35 mm movie cameras. The PL stands for positive lock . It is the successor mount to the Arri bayonet; however, unlike the bayonet mount, it is incompatible with older Arri mount lenses … Wikipedia
Four Thirds system — 4/3 redirects here. For 4:3 image aspect ratio, see Aspect ratio (image)#4:3 standard. Four Thirds logo The Four Thirds system is a standard created by Olympus and Kodak for digital single lens reflex camera (DSLR) design and development. The… … Wikipedia
PV mount — A PV mount is a lens mount developed by Panavision for use with both 16 mm and 35 mm movie cameras. It is the only mount offered with Panavision cameras and Panavision designed lenses, and since the company only rents its equipment, this is… … Wikipedia
Olympus PEN E-P2 — Type Micro Four Thirds, interchangeable lens camera Sensor Four Thirds System 18.00 × 13.50 mm Live MOS Maximum … Wikipedia
Konica — For the Albanian thinker Faik Konica (also known as Faik Bey Konitza) see Faik Konica Infobox Defunct Company company name = Konica company fate = merged successor = Konica Minolta foundation = 1873 defunct = August 5, 2003 location = Japan… … Wikipedia
M42 lens mount — Infobox camera mount mount name = M42 caption = Auto Takumar 1:3.5 35mm type = Screw external diameter = 42mm inner diameter = 41mm tabs = none flange = 45.5 mm connectors = Auto apertureThe M42 lens mount is a screw thread mounting standard for… … Wikipedia
Mirrorless interchangeable-lens camera — MILCs feature a large sensor in a small body (Olympus PEN E P2) A mirrorless interchangeable lens camera (MILC) is an emerging class of digital system cameras, intermediate between compact digital cameras and digital single lens reflex cameras… … Wikipedia
Four Thirds System — The Four Thirds System is a standard created by Olympus and Kodak for digital single lens reflex camera (DSLR) design and development.cite news | first= | last= | coauthors= | title=Kodak and Olympus join forces | date=2001 02 13 |… … Wikipedia