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M4 Light Leak


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I have a recently purchased M4 which leaks in a consistent way in the same place on the frame. I have added a strip of electrical tape along ghe bottom of the door on the back of the camera to increase pressure on this back plate (which hinges at the top), which has helped. The frequency and severity of the leaks is less, but not gone. I have an M-2 which has none of this leaking.

I have attached a jpg showing the issue, which appears to be happening, maybe when I hold the camera between thumb (on the back) and forefinger on the front, between shots. It looks like it occurs on the frame following the one in position for exposure at the time. See frames 29, 30, and 35 on the attached file, right above the frame numbers in the rebate area. (36 has a trace of this but not much) Imagine that the film is in the camera (inverted). The leak occurs at the very top left area of the seam between the door and the body, right where the fogged area is on each of these frames, on a frame which is next to be positioned at the exposure aperture.

Any suggestions, short of sending this to be repaired?

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I believe that this type of leak is described in M4 service manual, may happen as well in earlier models. Immediate remedy is tape at the top of back door, as LocalHero wrote. Permanent resolution I may post over the weekend when back at home

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Thanks for your responses. I know I can tape off the door and at least then know where the offending area is.

I don't see any foam areas around the hinge area, only some grooves or edges running up the right side that become light traps.

I'll be curious to see what Jerzy says about the M4 manual.

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Clearly the top hinge, as the streaks go across the sprocket holes from the lower edge of the picture, which is at the top of the camera (as the image is inverted on the film). I bought my M4 in 1968, and it developed a leak at the hinge also. At that time there was no foam used in the M4, but a stiff strip of black cloth was against the inside of the door hinge. It developed a wrinkle in my camera, allowing the light leak. Smoothing the cloth strip and lifting it up with the door removed allowed it to recover and be leak free for a few years before I had the camera serviced.

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here is extract from German Service Manual, it describes exactely this problem. Of course, the light seal may cause it as well, so  it shall be checked as well.

Service manual says, that the reason for this light leak is unsifficient sealing of the right backdor pin, the fixed one. On the photo below it is the left one. Light goes into the hole in back door, is being reflected from the movable pin and causes light exposure around /behind the second perforation hole.. Remedy is to seal the fix pin with black paint, usually I am painting as well the movable pin, where the arrow starts.

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