Sunday, 6 February 2011
Film, Reprocity and Pinholes
The issue that always crops up with pinhole photography is reciprocity failure. As exposure times go longer than about 1 second, you need to add more and more exposure time. Your meter tells you you need 5 seconds, but you’ll need to give it 30 sconds. Or the meter suggests 5 minutes and you’ll need 2 hours or maybe 5. It's hard to tell. With colour it can be worse as the colour balance of the film starts changing with longer exposures. It’s all a little imprecise. Trial and error becomes the standard technique.
So with a new pinhole camera to play with, I thought I’d visit the film manufacturers websites and see who advertises the best reciprocity characteristics. From their published data I've worked out a basic exposure guide for a few popular films for my f250 camera:
The yellow shaded areas are where reciprocity correction has needed to be applied. The deeper you go into the yellow, the more unpredictable the result. The grey area is beyond Ilford's published data. It's important to note that I've done no testing here, this is just from manufacturers data. Out in the real world, actual exposures might need to be completely different. You need to do your own testing.
And the winner? With no correction needed all the way down to LV8 it has to be Provia 400x. The 6x9 colour transparencies are going to look amazing! In black & white it's between Delta 3200 and TMax 400. I'm tempted to say Tmax as Delta at 3200 is already a push process. It's a just a shame Kodak don't do TMax 3200 in 120 format. That might work really well in a pinhole. Anyway, I'll be stocking up just as soon as I've made sure the camera actually works!