Investigating and diagnosing light leaks

After my recent experience with a light leak on a TLR and another leak on a compact 35mm, I realized that there was very little information online about how to go about diagnosing these kinds of issues and thus fixing them. Most of the tutorials online that mention “light leaks” seem just to talk about replacing the foam seals around the door; which is fine for a certain age of camera and if that is where the light is coming in.

With both of my issues this was unhelpful and so I thought perhaps I would share my thought process in tackling these leaks; apologies if this is a case of ‘teaching your grandmother to suck eggs’ and maybe a lot of this is obvious for some of you – please chime in if you have techniques I don’t mention.

So first off, if the foam seals are deteriorating then of course replacing them is a fairly simple and cheap exercise that is worth doing anyway and may well resolve the issue. In my case this was not required for either camera.

let’s begin

This is similar to a detectives process; looking at the evidence available, identifying suspects, eliminating as many as possible from your enquiries, gathering more evidence and hopefully finding the culprit.

Look at the negatives (evidence)

Take a good look at the negatives and see where on the film the fogging is affecting. If the fogging goes outside the frame then it is likely the leak is in the film chamber around the back of the camera. If it is constrained to within the frame then it is likely it is coming from the front of the camera from the direction of the lens. See these two examples;

This one from my Voigtländer Superb is definitely outside the frame

This one from the little Vito-C stops where the frame stops

Looking at the images will also give you an idea of the direction of the leak; for example, typically on a 35mm, fogging on the lower right means a leak on the upper left. I say “typically” as some cameras may vary. Make sure you know the route of the film through the camera; some feed film left to right and other right to left – so know your camera’s operation.

Lets look at the first example

I should note that this camera predates any sticky foam inserts and a previous attempt by me to add some foam had no benefit and put strain on the closure. Also examination (and the knowledge that light travels in straight lines) has suggested that the edges of the doors are as good as can be expected in terms of sealing and there are no bends or breaks observed.
What I notice looking at this negative is that not only does the fogging ignore the frame but it has a definite edge that is limiting it’s reach and is separate from the frame of the image; this can be further observed in the image at the top of the page.

What I deduce from this, is that the light is leaking onto the film at a point either before or after the frame has left the exposing area of the camera and, wherever that is, it has either an edge or some other masking which is creating an edge to the fogging.

To further diagnose I wanted to get another roll which would allow me to eliminate things from my enquiry and prove some theories. I shot another film this time with a small piece of (black) card on the take up side of the camera (after the frames had been exposed).
Note that this camera has a horizontal right to left path for the film (when looking from the rear) .
The card was intended to add some shielding and if it ‘changed’ the fogging would identify that area of the camera as the target area. I wanted the lab to leave the film roll in one piece (they cut it into short strips by default) so I could re-run the film through the camera and hopefully see the position of the fogging in relation to the physical layout of the camera.

Unfortunately the lab made a mistake and cut the film anyway but I was still able to make some progress. The black card on the take-up side had no impact and so I was confident that it was not leaking on that side.

When taking this roll, towards the end,  I ran a few frames through without taking any shots so I knew I’d have a section which had passed quickly from the unexposed to the exposed side of the camera with no images.

The film showed that the first of these blank frames had fogging whereas the other two had none. This told me that the first of those frames got fogged as the previous frame was being shot, i.e. while it was waiting to be wound into frame. The next two frames did not wait and went straight through and they did not get any fogging. I was pretty sure now that I knew the general area of leak but not the actual point.

Just to be sure, I moved the black card over to the take up side and shot another roll. Unfortunately as you may have already read elsewhere that film was a slight disaster as it was old expired film and, due to my miscalculations, all the shots were underexposed. On the positive side though, not one of them showed any signs of fogging outside the frame. Obviously the fogging has nothing to do with my exposure settings and so would be independent from the images. Now I was certain I was in the right area.

Maybe it’s time to ‘waste’ a roll

I have a couple of options at this point; to blindly start taping up areas of concern – shoot a roll and see if it fixed it (the trial and error approach), or try something designed to identify that actual problem

This is the plan;
Take a roll and load it into the camera (ideally in a dark area). Take a bright light source such as a torch (US: Flashlight) and systematically shine it through specific points on the camera in the area already identified as suspect; rolling the film on two frames between each test point. I would log each frame (or more specifically off-frame) against where the light was directed. Hopefully I would have a roll where one or two off-frames would have fogging and the rest not and I would know exactly where the leak was, based upon the log.

It would be a shame to use a roll and not get any pictures but as part of this diagnosis and the hope of resolving this last issue I think it is worth it.

I will let you know the outcome in another post….

Example 2

The Vito-C was slightly easier to figure out. From the image of the negative above, we have already identified the the fogging was part of the frame (not going out to the edge of the film) and so likely to be coming from the front. This means that (unlike with the TLR) we could do some examination with the back open and actually look.

I took the camera to a dark room and using my hands to shield as much as possible, shone a torch (US: Flashlight) around the front of the camera with my eye buried as deep into the back as possible.
What I saw was a tiny chink of light coming though in the top corner above-left of the lens – there’s my smoking gun! I experimented in moving the light and using my finger as a blocker to narrow down the specific point of light entry.

This camera has a lens that retracts into the body when the front is closed and it seems that the seals around the lens, are letting light in down the side.

I know now where the leak is coming from, next to resolve; which is easier said than done. There is little information (read “little” as “none”) available on how to disassemble this camera and so I will be working in the dark (pun not intended but acknowledged and appreciated).

Maybe a disassembly and fix will be the subject of another post, in the meantime I am testing whether just putting a small piece of foam inside the back where I can see the light coming in is enough to prevent fogging (without disassembly).

I hope that with these two examples and going through my thought process has been useful; I will update later with progress.

If you have ever done this sort of thing and have some further suggestions or tips, please do comment below.