Seth Baldwin Posted May 19, 2022 Share Posted May 19, 2022 I've been trying to find information on what the typical distance is from the mount of a PL lens to the last point of contact at the back of the lens. I'm not sure what this metric is called, I have attached an image below to help illustrate what I'm looking for. From my observations, it appears this distance varies across lenses. If it varies from lens to lens, do lens manufacturers abide by at least a max depth for how far the back of the lens protrudes from the PL mount? If I can't get an exact measurement, is there at least a ballpark estimate for say Arri Master Primes? Thanks, Seth Link to comment Share on other sites More sharing options...
Premium Member David Sekanina Posted May 19, 2022 Premium Member Share Posted May 19, 2022 (edited) it varies from lens to lens, usually wide angle lenses protrude further back, tele lenses less. there's a limit on how long it can protrude for film cameras because of the spinning mirror. The PL mount lens diameter is 54mm, so for a rough measurement you can measure the diameter on your image and calculate the scale multiplier. Edited May 19, 2022 by David Sekanina 1 Link to comment Share on other sites More sharing options...
Robino Jones Posted May 19, 2022 Share Posted May 19, 2022 What you're looking for is "Flange distance". https://en.wikipedia.org/wiki/Flange_focal_distance this wiki page says 44mm but you should double check that elsewhere.. you know wikipedia ? Link to comment Share on other sites More sharing options...
Seth Baldwin Posted May 20, 2022 Author Share Posted May 20, 2022 (edited) 5 hours ago, Robino Jones said: What you're looking for is "Flange distance". https://en.wikipedia.org/wiki/Flange_focal_distance this wiki page says 44mm but you should double check that elsewhere.. you know wikipedia ? Flange focal distance is the distance between the PL seat face to the image plane. I'm referring to the distance from the PL seat face to the last point of contact on the lens itself (for most pl lenses). I'm already aware the PL flange focal distance is 52mm Edited May 20, 2022 by Seth Baldwin Link to comment Share on other sites More sharing options...
Seth Baldwin Posted May 20, 2022 Author Share Posted May 20, 2022 (edited) 12 hours ago, David Sekanina said: it varies from lens to lens, usually wide angle lenses protrude further back, tele lenses less. there's a limit on how long it can protrude for film cameras because of the spinning mirror. The PL mount lens diameter is 54mm, so for a rough measurement you can measure the diameter on your image and calculate the scale multiplier. Thanks for the insight. Do you know what the rear lens element max protrusion limit is in millimeters from the PL seat face to the spinning mirror of super35 film cameras? I'm struggling to find this information online. Edited May 20, 2022 by Seth Baldwin Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted May 20, 2022 Premium Member Share Posted May 20, 2022 There is no standardised technical term for this that I'm aware of, I call it "rear protrusion" or "behind the mount protrusion". Flange depth or focal flange distance is a different thing, referring to the distance from lens mount flange to sensor or film plane. This differs for each mount standard, PL for instance is 52.00mm, EF is 44.0mm etc. As David mentioned earlier, every lens is different in terms of how far they protrude past the mount flange, but wider lenses typically protrude more than longer ones. The rear protrusion limit of older PL or Arri B or S mount lenses was dictated by the mirror shutter position. For this reason the safe protrusion space is more or less cone shaped. The following diagram is the safe protrusion area for the Alexa Studio, a digital camera with a spinning mirror/shutter, but it can serve as a guide for 35mm film movie cameras also. Note that 16mm lenses may protrude a little further than this, so never mount 16mm lenses to a 35mm film camera (or Alexa Studio) before very carefully checking that they clear the mirror at infinity. With digital cameras there is more room, but there are still baffles, sensor cover glasses and occasionally internal filter systems that limit the rear protrusion. The nominal 31.5mm depth illustrated above tends to be a limit most lens manufactures stick to as a maximum rear protrusion standard, which is also safe for digital cameras. Whether lenses or adapters fit can also depend on the diameter however, and different cameras will have different limits. Certain PL adapters for older Arri mounts for instance will foul on the inner baffles of PL mount Alexa cameras because they protrude more than about 20mm near the edge, even though they worked on PL mount film cameras. 1 1 Link to comment Share on other sites More sharing options...
Seth Baldwin Posted May 20, 2022 Author Share Posted May 20, 2022 44 minutes ago, Dom Jaeger said: There is no standardised technical term for this that I'm aware of, I call it "rear protrusion" or "behind the mount protrusion". Flange depth or focal flange distance is a different thing, referring to the distance from lens mount flange to sensor or film plane. This differs for each mount standard, PL for instance is 52.00mm, EF is 44.0mm etc. As David mentioned earlier, every lens is different in terms of how far they protrude past the mount flange, but wider lenses typically protrude more than longer ones. The rear protrusion limit of older PL or Arri B or S mount lenses was dictated by the mirror shutter position. For this reason the safe protrusion space is more or less cone shaped. The following diagram is the safe protrusion area for the Alexa Studio, a digital camera with a spinning mirror/shutter, but it can serve as a guide for 35mm film movie cameras also. Note that 16mm lenses may protrude a little further than this, so never mount 16mm lenses to a 35mm film camera (or Alexa Studio) before very carefully checking that they clear the mirror at infinity. With digital cameras there is more room, but there are still baffles, sensor cover glasses and occasionally internal filter systems that limit the rear protrusion. The nominal 31.5mm depth illustrated above tends to be a limit most lens manufactures stick to as a maximum rear protrusion standard, which is also safe for digital cameras. Whether lenses or adapters fit can also depend on the diameter however, and different cameras will have different limits. Certain PL adapters for older Arri mounts for instance will foul on the inner baffles of PL mount Alexa cameras because they protrude more than about 20mm near the edge, even though they worked on PL mount film cameras. Exactly what I needed, thanks Dom Link to comment Share on other sites More sharing options...
Premium Member David Sekanina Posted May 20, 2022 Premium Member Share Posted May 20, 2022 (edited) Dom, do you know if this is an official document from ARRI? I'm asking, bc the mirror on ARRI (and Aaton) cameras is tilted at 47.5 degrees, so the reflected beam off the mirror is angled at 5 degrees off the vertical axis, to make space for the ground glass housing, for it to not protrude into the film gate. I redrew quickly these dimensions to show the differences: As a rough envelope it's probably good enough though Edited May 20, 2022 by David Sekanina Link to comment Share on other sites More sharing options...
Premium Member David Sekanina Posted May 20, 2022 Premium Member Share Posted May 20, 2022 Silly me, they probably used the 45 degree limit line because of the ARRI 35 II and III, which had their mirror sideways, tilted at 45 degrees. Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted May 20, 2022 Premium Member Share Posted May 20, 2022 15 hours ago, David Sekanina said: Dom, do you know if this is an official document from ARRI? The drawing is from the Alexa Studio manual, so yes, it’s official Arri literature. I’ve never seen another document describing this clearance, but I assume lens manufacturers must have been given some sort of guide during the film era. Many lenses (particularly 16mm ones) had bevels machined into the rear housing to clear the mirror, so manufacturers were using every last mm available to them. The envelope shrunk after the 16St, causing some lenses to become unusable (Cooke Kinetals) while others went through modifications in order to clear the newer cameras (certain Schneider’s). 1 Link to comment Share on other sites More sharing options...
Premium Member David Sekanina Posted May 21, 2022 Premium Member Share Posted May 21, 2022 Thank you Dom! Aaton had a patent for the recess in their rotating mirror, so they could move the hard front closer to the film plane.Theoretically you could have lenses that protrude a bit further in that area into the camera than with ARRI cameras, that all have flat mirrors from center to outer diameter. But lens makers stuck to ARRI's norm. Image by Charles Pickel Link to comment Share on other sites More sharing options...
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