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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; unlike the bayonet mount, however, it is incompatible with older Arri-mount lenses, due to the larger diameter. (This can be rectified with an adapter relatively easily, as the flange focal distance is identical.)
The mount contains four pronged flanges that each contain a notch towards the center. Any of these four notches can be used to align the mount to a locating pin located approximately 45 degrees clockwise from the top of the camera's lens mount. This means that the lens can be oriented in any of four different configurations, which may be decided by factors such as focus puller position, camera position, and preference to working with meters or feet (if a lens has different line indicators on each side). The mount is locked into place using a friction locking ring that, in conjunction with the four prongs of the flange, creates a very strong lens seating. This has become a crucial factor in recent years, as bigger lenses with zoom capabilities, longer focal lengths, or larger lens elements have increased the need for mount stability due to the greater stress placed upon the mount by these devices.
Furthermore, the tendency is for flange focal distance to become a more critical factor as sharper lenses, film stock with higher resolving power, and post-production workflows that preserve more of the original camera negative's information continue to make technological progress and advancement. Flange focal distance is also more likely to be rigorously checked as tastes for wider angle lenses continue to push the envelope, as wider lenses have a much narrower tolerance for lens displacement.
- Flange focal distance: 52.00 mm (51.97 mm for the Arri SR high speed models) (73.5 mm for Arriflex 765, that mount is known as "Maxi PL-mount")(60.00 mm for XPL-mount on ALEXA65) (44 mm for the LPL-mount on ALEXA LF)
- Diameter: 54.00 mm (64.00 mm for Maxi PL-mount) (72.00 mm for XPL-mount on ALEXA65) (62 mm for the LPL-mount on ALEXA LF)
- 35 mm: Arriflex 35III (later models), Arriflex 35BL3 (later models), Arriflex 35BL4, Arriflex 35BL4S, Arriflex 535, Arriflex 535B, Arriflex 435, Arriflex 435ES, Arriflex 435 Advanced, Arriflex 435 Xtreme, Arricam ST, Arricam LT, Cinema Products FX35, Moviecam SuperAmerica, Moviecam Compact, Moviecam SL, Aaton 35
- 16 mm: Arriflex 16SR2 (later models), Arriflex 16SR3, Arriflex 16SR3 Advanced, Arriflex 416, Aaton XTRplus (standard), Aaton XTRprod (standard), Aaton A-Minima
- 65 mm: Arriflex 765, ARRI ALEXA65 (uses the XPL-mount)
- Digital: Arri Alexa, Arriflex D-20, Arriflex D-21, ALEXA65, ALEXA LF, Dalsa Origin, Dalsa Origin II, Sony F35, Sony F65, Phantom, Canon C300 PL, AJA Cion, Blackmagic Design URSA, Blackmagic Design Cinema Camera PL
- PL-mount available with an adapter: Ikonoskop A-Cam dII, Silicon Imaging SI-2K, Sony F3/F5/F55, Blackmagic Cinema Camera mFT/Pocket Cinema Camera
- PL-mount available with a third-party adapter: Sony α7S, Panasonic GH4
- PL-mount optional by user choice: Canon EOS C300, Canon EOS C500, Red One, Red Epic, Red Scarlet), Digital Bolex (uses interchangeable mounts), Blackmagic URSA Mini Pro (uses interchangeable mounts)