What is it with These Light Leaks all of a Sudden? Systematic Errors

What a day the other day. Finally out taking photographs after a month of lousy weather. Not the best conditions but a very nice morning to be outside. No rain and light intermittent wind and increasingly cloudy. I took a few photos and ended up with at least 2 with light leaks! The color ones probably have them as well. What is going on?

Lots of things rush through my head. Camera problem? (Intrepid 4x5 mkIII). My new second hand film holders I got for a bargain price? Film loading problems?

The trouble is I have used the Intrepid quite a lot and while there are aspects of its build quality and smoothness I might criticize I have been taking a a lot of photos without many problems. The film backs I had seen one or two possible problems, but I wasn’t able to nail down one particular unit.  I had taken to photographing the film backs with my phone after a shoot to record which film came from which back for just such a contingency.

I googled for problems with the Intrepid but most of them seem to be teething problems with earlier models or specific units that had not been built well.

More generally there was talk about film holder technique and issues pull dark slides or not getting the film holder seated properly. This is possible though I am careful but perhaps I have gotten cavalier.

I went into the darkroom and put a bright light into the lens board hole and in complete darkness looked carefully while loading a film holder and pulling the dark slide.  No, technique did not seem to be the culprit. Any tendency to pull the film holder away fro the camera would take enough effort I felt it would have been obvious at the time.

The Glimmer of an Answer

I did see very faint slivers of light where it was leaking from under the film holder where it mates to the back plate of the camera.

My immediate thought was disappointment. I mean this is supposed to be a light tight system. The mating surfaces were perhaps not flat or smooth enough. My first thought was to place a strip of black felt along the side of a the back where the film back slots in. This would take up some of the slop that allows the film back to slide back and forth. I did this and it seemed to cure it. It is a tight fit for the ground glass holder so I would need to be careful it is seated properly. I am concerned this fix may introduce a chance of focusing errors. Not optimal. I  have not opted to do this yet as I have propose other remedies at the end of the post.

Felt strip solves light leak but ground glass does not seat easily.

I next made a small sanding block with 1000 grit paper attached and carefully and evenly sanded the landing area of the film back. The was routed away with a CNC router and is not entirely flat and smooth. This is where I am seeing the light leaks. I then painted this area with black paint which I gain sanded smooth. Tests indicated some improvement but not a complete success.

I did some more online research. I came across an old-timer’s comment on the Large Format Photography forum. He asserted one needed massive dark cloths (up to 8x10 feet). He and many well known photographers used large cloths to cover the entire camera up to the lens and all work with film holders happened under what I can only imagine as a kind of tent. It solves all kinds of problems from leaky bellows to old and fragile film holders and well worn cameras. Probably especially useful mid-day in the American Southwest. I can only image what a gust of wind would do and all of the dust and muck picked up by the thing. Sorry, I am not quite that desperate (yet).

This got me to thinking about my own particular circumstances. I had recently purchased a new purpose-made dark cloth online. Prior to this I used a micro-fiber towel about 2x3 feet in size. I clipped this to the camera using bulldog clips. I decided a ready-made item might be better. The towel was not stiff enough and constantly draped into my view of the ground glass. The new cloth has a band of elastic and Velcro to close it. Except part of the Velcro is on the wrong side which I had to fix. The elastic is a bit tight for my liking as well. Anyway I digress.

It dawned on me that a couple of things are going on now. 1) I have changed my working methods, 2) Conditions may make this problem more likely. This was sounding like what is referred to in science and engineering as a systematic error. That is a problem imposed by the techniques that repeated creates the same problems.

Systematic Errors

With the new dark cloth I have taken to removing it completely after composition and focusing were complete. This is contrary to the old timer’s advice above and my previous practice with the micro fiber towel. The other day the wind and clouds meant I was often waiting for the wind and light to come together at the right moment. There sat my camera, uncovered in bright daylight for 15 or 20 minutes or more. Now I could see how a very small leak might become an intermittent problem. Thinking back to to some earlier failures these too were likely times I waited to take my shot and perhaps had removed the dark cloth then too. A couple below. These were complicated by the fact they were taken on expired film that had been kept refrigerated. This gave me something else to consider as the source of the problem. 

Expired Astia Test made me think the expired film was bad. Subsequent images were OK though.

This day was very windy and I had to wait to limit reed movements in the foreground. 

Light leak on left edge all other images that day OK. (bad film holder?)
Probably caused by the sun having risen and then waiting for the wind to die to limit tree movement. 

So I think I have a resolution. Not sure if I should be dissatisfied with my camera owing as it does exhibit small leaks. Reading online there seem to be a couple of camps in this regard. One holds the equipment is faulty if it leaks any light. The other states that these problems are inevitable and prudence suggests using the dark cloth as protection. It may well be that those who think their equipment is consistently light tight have circumstances or habits that avoid the problems.  It certainly does not hurt to develop better habits for the day when you do have equipment failure.