Repair Guide / Light Seals
Light Seal Replacement
Replacing the foam light seals on 35mm and medium format cameras. The job most used cameras need before you shoot a single roll.
Overview
Light seals are the foam strips that prevent light from entering the camera body around the back door. They're made of open-cell foam that degrades over time, turning from firm black foam into a sticky, crumbling residue that gets on the film and causes light leaks.
In Florida, the combination of heat and humidity accelerates foam degradation significantly. A camera that might last twenty years in a dry climate may need new seals after ten years here. I replace the seals on every camera I buy, regardless of apparent condition.
The job is not difficult. It requires patience, a steady hand, and the right materials. The most important thing is removing all of the old foam before installing the new material. Any residue left behind will cause the new seals to fail prematurely.
I use self-adhesive felt for most seals. It's more durable than foam, easier to work with, and available in the correct thickness. For cameras that require very thin seals, I use thin foam from a dedicated light seal kit.
Tools needed
Procedure
Open the camera and assess
Open the camera back and examine the existing seals. Note their location, thickness, and condition. Take a photograph before removing anything -- it's useful to have a reference when installing new seals.
Remove the old foam
Use a toothpick to scrape out the old foam from the channels. Work carefully to avoid scratching the camera body. The foam will come out in pieces. Get all of it.
Clean the channels
Dampen a cotton swab with isopropyl alcohol and clean the channels where the old foam was. Remove all residue. The channels need to be clean and dry before installing new seals.
Cut the new seal material
Cut strips of self-adhesive felt to the correct width and length for each channel. The width should match the channel width exactly -- too wide and the seal will bunch up, too narrow and it won't seal properly.
Install the door hinge seal
The hinge side of the camera usually has a narrow channel that requires thin material. Install this seal first. Press it firmly into the channel with a toothpick.
Install the door edge seals
The two long seals that run along the top and bottom of the door opening are the most important. Cut them to length and press them firmly into place. Make sure the ends meet the corner seals cleanly.
Install the corner seals
The corners of the door opening often have small foam pads. Cut new pads to the correct size and install them. These are easy to overlook but important.
Check the mirror box seals
On SLR cameras, there are additional foam pads inside the mirror box. These degrade at the same rate as the door seals. Replace them at the same time.
Test for light leaks
Load a roll of cheap film and shoot it in bright sunlight, paying particular attention to the edges of the frame. Develop the film and check for light leaks. Any fogging at the edges indicates a seal problem.
Warnings
Do not use the camera until you've verified there are no light leaks. Shoot a test roll first.
Isopropyl alcohol can damage some camera finishes. Test on an inconspicuous area first.
Do not use foam that is too thick. It will prevent the camera back from closing properly and can damage the hinge.
In Florida, replace the seals more frequently than you would in a dry climate. The humidity here accelerates degradation.
Notes
I buy light seal material in bulk from dedicated suppliers. The kits sold for specific camera models are convenient but expensive. Bulk felt and foam is cheaper and works just as well.
The thickness of the seal material matters. Most 35mm cameras use 1mm to 2mm foam. Medium format cameras often use thicker material. Measure the channel depth before cutting.
Some cameras have seals in unexpected places -- around the film door latch, around the rewind knob, around the film counter window. Check the entire camera, not just the obvious locations.
I've replaced seals on cameras that looked fine externally and found that the foam had completely disintegrated inside the channels. Always replace them on any camera that hasn't been recently serviced.
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