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I recently used a rental RB67 and in looking at the 120 negatives I have noticed a pattern of two types of probable light leaks across all of the film that I shot (but fortunately only across some images in each roll). As it was a rental I no longer have that camera so the issue can't be fixed, so I'm just looking for a probable cause.

In the first case, there is a dark band covering the numbers along the bottom of the negatives. This only seems to occur on the last 3 or so images on the roll, and curiously this also only seems to occur on one edge of the film.. I suspect that when I removed the film from the camera that I didn't keep the wrapper tight. Is my assumption correct?

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The second issue I have noticed is a probable light leak on one corner of some frames. There doesn't seem to be any pattern in which frames have this leak. The only explanation I can come up with is that I was changing lenses and that mirror was not perfectly sealing the film (and I wasn't using the dark slide when changing lenses - is that a bad thing?) But when I look at the images on either side of the affected one, they were all taken with the same lens. This may be explained by me swapping the lens to test the field of view and then going back to what I originally had. So any ideas on this leak?

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    \$\begingroup\$ Best practice is to always use a dark slide when changing lenses with a Mamiya RB67 and similar cameras that have the shutter in the lens, rather than the body. Yes, the mirror assembly is supposed to prevent light leaks, but what is allowed through a lens is a much narrower cone of light that what is allowed through the opening in the mount flange when a lens is not in place. \$\endgroup\$
    – Michael C
    Feb 11, 2020 at 9:45

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The first light leak along the edge of the film is either caused by the film not being wound tight enough onto the spool, or the spool itself not being completely opaque. Since only the last part of the film is affected, the film is likely not wound tight enough. That can be a problem with the film holder, or that you were a bit sloppy when unloading the film. As long as the light leak does not reach the exposed frame, it is not really a problem, but I usually wrap exposed 120 films in aluminium foil to prevent such problems at all. Both unexposed, as well as exposed 120 rolls are prone to such light leaks.

The second light leak looks as if the pressure plate in the film holder might not hold the film tight enough. There is likely a small gap between the film and the opening for the exposure in the back of the camera. This is also not really a problem, since the unintentional exposure is only outside the actual image frame.

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  • \$\begingroup\$ I agree with you about the first one. For the second one it only occurs on some frames and is not consistent. But there are some frames where it has occurred within the corner of the frame itself (It was easier to show it outside of the frame) \$\endgroup\$
    – Peter M
    Feb 10, 2020 at 13:59
  • \$\begingroup\$ @PeterM It is impossible to guess without seeing the camera. On the negative you show, the light leak was only obvious outside the intended exposure frame and if the film is held properly against the back plate of the camera, no light should get there even if a closed mirror lets light through. \$\endgroup\$
    – jarnbjo
    Feb 10, 2020 at 15:08
  • \$\begingroup\$ OK .. I see what you mean about the back plate. So the light leak is from somewhere behind what ever masks off the surrounds of the frame. EG this could be from the pressure plate not being 100% flat. Could it also be due to sloppiness in the rotating back? \$\endgroup\$
    – Peter M
    Feb 10, 2020 at 15:27
  • \$\begingroup\$ @PeterM Yes, exactly. There is a mask, either in the back of the camera or at the front of the film holder, against which the film is pressed by the preasure plate, so that the film should not be exposed outside the intented frame. There are also several light seals in the film holder. The seal foam may have dried, so that the seals do not work properly. That would be my bet, but impossible to say without inspecting the holder. \$\endgroup\$
    – jarnbjo
    Feb 10, 2020 at 16:49

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