Folks, An old, old topic I know but please indulge me as I put my own spin on the topic. I just got my Canon IID1 and IVSB2 back from a very reputable repair facility where they were both CLA'd and shutter curtains were replaced (with Leica curtains, nonetheless!). Being anxious to shoot them for real, I thought it prudent to test them so I stuck them on tripods and burned through a roll of film in each. All I had lying around for consumer-grade film was 36 exp, 400 ISO, color print film. Since I had 36 exposure rolls, I figured I'd switch around lens for my test shoots. With my more modern film cameras (Canon FD/EOS, Leica M7), I always am sensitive to making sure I never remove the lens in direct sunlight. In this case, the cameras remained on the tripod, in the outdoor light but never FACING the sun, while the lenses were swapped. I took notes on lighting conditions -- metering ambient light at the subject was F16 @ 1/250s (ISO 400). Since the cameras were stationary, I had the lenses nearby and walked over to get them when performing the swap. There was no lens on the camera for probably 30 seconds between swaps. When the film was processed, I noticed light leaks on the frames following every lens change on both cameras. Sometime the leak/streak would be present in smaller form on the NEXT frame as well. No other light leaks elsewhere though. I talked to the person servicing my camera and he gently reminded me that these RF's -- Leica (thread mount) as well as Canon -- had very little light baffling around any of the interior mechanisms and that, although he was willing to check the cameras out for me, it was probably something I should expect just due to the design of cameras of the time (early 1950s). I do trust his advise and I'll test again in more subdued light but I thought I'd float the topic by this group and see what your thoughts were. Gut feel (prior to my phone call to the service person) was that I expected them to be sensitive to light leaks and never to face them toward the sun, but I did believe you could change lenses outdoors. Now something I failed to consider prior to my test was the fact that I was using ISO 400 film. I'm not sure I ever shot that fast of film in these cameras before. One camera was my Dad's and although I remember him changing lenses outdoors long ago, he was probably shooting K25 or K64 -- far more forgiving for light leaks. I just wanted to toss the topic out and get the group's thoughts on this. Are your old RFs as vulnerable to light leaks as mine are, based on my short story? Thank you!