Advice on possible light leak issue.

[Josh]

Hi, sorry if this isn't the right sub. I couldn't think which would be more on topic.

I bought a camera and took some photos on some old (expired 2006) polaroid film. I've now got some film, but the polaroids gave significant cause for concern. There is a very visible light mark across the centre of almost all of the images, going across the width of the film. My immediate thought was that this was a light leak, so I carefully check over the bellows with a torch looking for holes. I couldn't find any. So I tried another exposure with the focusing cloth tucked close to the bellows. They still show the mark and the mark is at almost exactly the same place. On one exposure, where I seemed to have massively underexposed the image (centre top - I believe from not removing the evelope for the polaroid, but I'm not 100% sure) the mark is very clearly defined, so in photoshop I cut it out and matched it up to some of the other images, setting the layer type to subtraction. It seems to remove almost all of the mark. I think that the three images (the bamboo image was taken on a different day and outside) had different levels of movements so I'm not convinced that this is a light leak, as I'd expect that to move around relative to the bellows. To complicate that further, one of the images (left second row) was taken with a macro bellows - which I have also check for light leaks.

My question is: is this likely an issue with the polaroid film/back or is it some strange light leak? I wanted to sort this out before using film as it is much easier to check and adjust with polaroid film. I only have one polaroid back, so if there is some kind of issue with it then I don't have a way of checking.

In a last-ditch attempt to work out what might be wrong, I pointed an dSLR at the ground glass and took an exposure correctly exposing the image formed on the ground glass at f/32. My thought is that if there was a light leak, it would make up the same relative exposure and so be visible. I did not see the mark on the ground glass (the framing is very different in the last image. The light used was much further out of frame, and I'm quite sure it is not the cause of the issue as it wasn't present in all of the exposures).

Thanks for any help or advice you have.