Saturday, September 7, 2013

Unsafe Light

I had had a couple of failures using Kodak CSG x-ray film in my pinhole camera. They came out WAY over-exposed. One was this photo of Jim's Beemer. I had a nagging suspicion in my head that the problem was with my safelight. I used a 3-LED headlamp. It is pretty bright, but I usually point it at the ceiling and not directly at the film. However when I was developing these, I had shone the light right down into the developing tray. So I needed to do some experiments. What if I cut, loaded and developed in complete darkness? That would give me information about the safelight variable. I was also curious about whether the film had somehow changed or maybe the pinhole had been damaged and I was over-exposing in the camera. So I took the same photo twice; once at my 'normal' calculated exposure (47 sec in this case), using iso 80 for the CSG. Then I took another photo one stop down (24 sec). This would tell me something about the accuracy of my exposure table. So here are the results.
x-ray-compare
I developed these together in the same tray of 1+100 Adonal for 4 minutes in complete darkness. Don't mind the scratches. I wasn't being particularly careful with this film, I just wanted to get an idea of the exposures. You can see that both exposures are passable. The one stop 'push' came out with a bit more contrast as you would expect, but both negatives are of normal density.
So I think I narrowed the problem down to the safelight. The LEDs must just be too bright. It could also be a wavelength thing. I am not sure what the spectrum looks like for these led lights. They might have an overlap with the sensitivity of the x-ray film even though it is classified as 'orthochromatic'. Anyway, there you have it. X-ray film will be developed in the dark from now on and I will continue to use my same old pinhole exposure chart with this film rated at iso 80 or 100.