reciprocity failure

[Robert Vigurs]

Shooting in the Redwoods today. 8x10, outdated Arista 125, metered at 64, black and white. 250mm, 6.7 Fujinon lens. 8" bellows extension. I metered for detail in shadows at zone 3. I gave it 2.5 minutes, f64 Made two exposures. Back at the darkroom, I used HC-110, and pushed the developing time to 8.5 minutes at 68 degrees. My negs are thin. I have obviously omitted the reciprocity failure factor to my exposure. I am going to try again tomorrow. Any ideas on exposure time to compensate? I'm thinking 5-6 minutes? Some reciprocity tables say more. I'd appreciate any input. Thanks guys.

[Jon Shiu]

Hi, you are only giving about 1 stop more exposure, which would still give thin neg. Probably 3 to 4 stops are needed. Try more like 20-30 minutes.

Jon

[Brian C. Miller]

Arista reciprocity info (pdf), from Freestyle.

Oh, ow, does this film ever have reciprocity failure! 2.5 minutes = 150 seconds, reciprocity correction would be at least 1500 seconds (25 minutes), or open it up by three stops.

[Robert Vigurs]

I thank both of you for your replies. I will shoot again tomorrow, same time, same place, camera and lens. Learning process here. I thought of you today, Jon as I used my 5x7 up near Pescadero, on the San Mateo coast. I remembered your image of the crab shell. So many beautiful small shells, and a dried stream of smooth rocks in the sand leading to the sea. I will go back there after a fresh morning rain, once the low tide comes at morning light. Again, my thanks.

[Brian Ellis]

The reciprocity table I use was obtained from John Sexton and it's been right on for me when using non-T Max film. His table shows 2 minutes metered = 5 minutes actual and 4 minutes metered = 24 minutes actual. So roughly interpolating 2 1/2 minutes from there, I'd probably expose for about 9-10 minutes for a metered 2 1/2 minutes. When you start getting up into 10 minute times reciprocity failure is really galloping along so the chances of overexposing just by adding a minute or two are pretty minimal so you might want to go as high as 12 minutes. And of course you'll have to significantly reduce your development time (to something like N - 3) to take the added contrast into account.

I often find that placing the darkest important shadow on Zone III results in a somewhat underexposed negative. For that reason I often place it on Zone IV. You might try that too.

[Robert Vigurs]

Thanks for that information Brian. I will look at putting the shadow areas in zone 4 next time. It makes sense when shooting in a shadowed Redwood environment. I did return today with the 8x10, same film. This time I gave 27 minutes exposure, f64, on two sheets. I achieved a much better result. Quite usable for the carbon process with which I am working. On a third exposure, where there was more sunlight on a small stream running through the grove, I went with 5 minutes at f32. Also a good registration of the light on the film. Could have gone with seven but didn't want to blow out the highlights of sun on the stream. A nice environment to teach myself these skills. Quiet. Ravens in the trees. Best way to learn is to do. I appreciate all of your responses. Robert