Fomapan 100 Death Spiral? Lessons in Reciprocity Failure
I was contemplating other ways of explaining the problems of underexposing film as discussed in an earlier post. One thought experiment was to use reciprocity failure to exagerate the effect. This lead me to recall Fomapan 100’s atrocious reciprocity failure and to speculate there may be a ‘death spiral’ for shadows under certain conditions of reciprocity failure. Indeed the few times I used this film in large format I found it very contrasty with thin shadows. This also lead me to read up more about reciprocity failure and I learned and confirmed a few other things.
Let's start with the Fomapan 100 Reciprocity correction...
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| Fomapan 100 Reciprocity Correction (hat tip Magna Images) |
My thought experiment is as follows…
Assume you meter a scene and Zone V and at the desired aperture this leads to a 1 second shutter speed. This is not unusual in my large format experience. That means Zone IV would have 1 stop less light and zone III would be 2 stops less light. Zones IV and III is where you would expect some detail in the shadows.
Now Fomapan 100 reciprocity at 1 second says you need to expose for 2 seconds. That means the other zones will also get exposed for the same 2 seconds. But Zone IV has half as much light. Fomapan 100 requires 7 seconds for 1 stop less light at 2 seconds which to my way of thinking means it wants more exposure (not 7 as this would bring the tone up to Zone V). All the way down the lower zones. This is what I have to call the reciprocity failure death spiral. If I am right it seems that there will be almost no chance of shadow detail or tone in zones IV and lower as each one actually gets exposed less than it would if we were not in shutter speed ranges where reciprocity failure were not a problem like 1/100th of a second.
The conclusion I take from this not to touch Fomapan 100 for exposures a second or longer. This means it is really inappropriate for large format where the slow film speed and small apertures frequently add up to long exposures.
Other Learnings
While contemplating this it occurred to me that correcting reciprocity failure at the lower end of exposure zones means overexposure in the highlights (since you are overexposing the whole film to compensate). It turns out this is exactly the case. This increases the contrast as the highlights intensify compared to the shadows. Further research reveals that this is the case even in films small reciprocity failure corrections. The result is that Kodak recommends about 10% less development for each stop of exposure correction (for Tri-X 320 and 400 films). Ilford says nothing about it but apparently the same figure works for Ilford films.
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| Kodak Reciprocity BW Development |
Finally it turns out this effect is can be used. As mentioned before reciprocity failure increases contrast and so can be used to increase the contrast of images that are low contrast. You just have to set the exposure so the film is in the reciprocity failure range and don’t compensate the development.
My Cheap Ektachrome
On a side note I bagged a lot of old Ektachrome EPN 4x5 film. My first couple of images with this film indicated I got lucky in that it seems it was freezer stored as the seller stated. My more recent images had a strong blue/purple cast which surprised me given the earlier images. It occurred to me this earlier Ektachrome might have different reciprocity failure than the current version. Indeed it does and is actually not very useful slower than 1/10th of a second and the images in questions were about 4 seconds. This will make it a challenge to use.
However I do like the look of the second image below which I described originally as having a painterly quality. So I may have to consider the artist aspects of shooting the film in the 1/10 to 1 second range.
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| Kodak Reciprocity Statement for Ektachrome EPN |
Below is a progression of 'raw' scans of different exposures on this Ektachrome EPN film. These scans have no gamma curve applied or any color correction. They are presented in increasing exposure. No compensation for reciprocity failure was made as I understood at the time that Ektachrome has none this far out. (Wrong for the older EPN. Modern E100 goes to 10 seconds with no recommended correction.)
In each case I provide a link to the final image to see the potential of each image realized.
The first image shows why I thought the film held promise. No color cast was apparent with nice dark black shadows. 1/8 second is supposed to require longer exposure and a color correction filter.
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| Ektachrome EPN at 1/8 sec exposure (Final Image) |
The next two I am verging on the 'not recommended territory of about a second of exposure.
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| Ektachrome EPN at probably less than 1 sec (no notes) (Final Image) |
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| Ektachrome EPN at 1 sec exposure (Final Image) |
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| Ektachrome EPN at 4 sec exposure (Final Image) |
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