Focal Plane shutter
Light Leak Testing.
It can happen that your negatives are fogged after exposure. Look where these leaks are clearly visible on the negative and think! There are some possibilities: The camera may have a light leak and the holder may have a light leak. Or even both. So the best thing is to use a new film holder to exclude the holder being the cause of the trouble. Then the camera remains as being the culprit. The most obvious cause would be that the bellows has one or more pinholes. In that case the negatives looks fogged almost all over the film, not specific on a certain spot. You may try that out by shining with a torch inside the bellows while the room is darkened. Small pinholes can be repaired with a good quality black self adhesive tape on the outside. Use tape that matches with the surface of the bellows. How to tackle this problem see:
More difficult is finding the light leak in the camera. In that case the negative may show a horizontal or vertical light stripe. Sometimes on one side, left or right. Sometimes just a small fogged part on one of the sides or even on top or bottom of the neg. There is only one way to find out what is wrong and that is to test with real film. Load the film-holder on both sides with film. To be sure what is left and right or up or down, always place your film with the notch to the right upper side into the holder. Place the camera - without the film holder and without the focusing ground glass- in a dimmed room. Remove the lens board with lens and draw the bellows half way out. Now take an electronic flash and fire inside the bellows while keeping an eye on the camera back, especially around the back frame area and the curtain of the focal plane shutter. If you can see flash light protruding, than you probably have found your light leak. Use black mat tape or something else like black velvet to repair the leak. Check everything carefully and check again. Now if you are convinced you found the leak and repaired it, place the camera on the table and close both shutters. Place the film holder including two unexposed films with the #1 film to the front and draw the dark slide. Take your flash and fire flashes on the camera from all directions. Close the dark slide. The second test should be done to ensure the good working and light leak proof of the focal plane shutter. Slide the film holder out of the camera and replace the holder with #2 to the front. Open the front shutter by setting the rim selector to "T" and trip. The shutter should stay in "Open" position. Select and set the diaphragm. Go outside in the daylight and select the exposure time on the dial of the focal plane shutter and wind the focal plane shutter. Your camera is ready to take a photo. After exposing #2, develop both films. If film # 1 is completely blank it proves that no light has entered the film holder. If number 2 shows an acceptable nicely exposed photo, you may presume that you found and repaired the light leak.