Fomapan 100 reciprocity: excessive.

retina_restoration

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I've got an app for calculating reciprocity for long exposures, and in general it gives me accurate data. However, when it comes to Fomapan 100, it's way off. If I use the values it suggests, I get severely overexposed negatives. Like, 2-3 stops overexposed. I've often seen these values quoted here on Photo and elsewhere, and the app I use gives these exact same values.

1s = 2s
2s = 7s
4s = 21s
8s = 59s
16s = 2m 32s
32s = 6m 17s
64s = 15m 15s
128s = 36m 13s

I had measured a scene two days ago, giving an exposure of 15 seconds at f16. I made two exposures on 5x7" Fomapan 100: one for 2 minutes and one for 3 minutes. Both were severely overexposed. I could barely get a usable image out of the 2 minute sheet. (It took a lot of post processing tweaks to get this.)

So, the example times posted above were found here on Photo nine years back. Do any of you know if there are updates to the Fomapan 100 reciprocity data that are more accurate? Thanks.
 

miha

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@Ian Grant reported earlier that the reciprocity failure is nowhere near what even Foma themselves suggest. Hopefully he can chime in here with more details.
 

koraks

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retina_restoration said:
Do any of you know if there are updates to the Fomapan 100 reciprocity data that are more accurate?
Click to expand...

No, but like you, in my experience the reciprocity failure is overstated in the documentation. I've never done really long exposures on this film; up to a minute or two at most. It's been a while, but I would usually apply a correction of 1-2 stops at most.

I've always found reciprocity correction a bit of a moving target anyway, since the is strictly speaking not even across the frame. The high values suffer less than the low ones, so IMO a reciprocity correction would ideally take into account on which values the emphasis is in the image.
 

loccdor

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Foma films are commonly believed to achieve less than box speed, yet at the same time it's the only negative film advertised as having more underexposure latitude than overexposure.

Its wide exposure latitude permits rating the film at +1 EV to -2EV with no change needed when processing in standard chemistry, making it suitable for working in a wide variety of lighting conditions.
Click to expand...

There must be something to that.

At least in my hybrid workflow, it's not a film I think looks good with overexposure.
 

RalphLambrecht

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using your empirical data one can calculate the average reciprocity failure coefficient p is approximately 1.82 fouse for the equation: expp = expm × (expm)^(p-1), where expm is the measured exposure time and expp is the required exposure time
 

RalphLambrecht

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RalphLambrecht said:
using your empirical data one can calculate the average reciprocity failure coefficient p is approximately 1.82 fouse for the equation: expp = expm × (expm)^(p-1), where expm is the measured exposure time and expp is the required exposure time
Click to expand...

So with p = 1.82, you can use Schwarzschild's formula for future reciprocity corrections:

expp = expm^1.82

This coefficient suggests fairly significant reciprocity failure - your film/sensor requires substantially longer exposures as the measured exposure time increases. For quick reference, with p = 1.82, some common corrections would be:

  • 10s → ~63s
  • 30s → ~4.7 minutes
  • 60s → ~14.5 minutes
This p-factor should work well for interpolating exposures within the range you tested (1s to
 

koraks

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RalphLambrecht said:
This coefficient suggests fairly significant reciprocity failure
Click to expand...

Yes. The question at hand here is whether the reciprocity failure is as bad as the numbers suggestion. What's your take on this for Fomapan 100 specifically?

loccdor said:
At least in my hybrid workflow, it's not a film I think looks good with overexposure.
Click to expand...
Fomapan 100 tolerates overexposure by a few stops, but at some point as you start to push part of the image data onto the curve, things tend to flatten off in a problematic way. For me, it has always worked OK if I rate it at 50.
 

blee1996

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I had similar experience, that the reciprocity table is excessive. I did some large format pinhole with the Foma 100 (Arista EDU Ultra 100), and they were severely over-exposed. Later I just rough estimate it by myself, and try not to exceed several minutes. At least for pinhole photography, I don't need all the details in the shadows.
 

revdoc

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I've used Foma 100 with pinhole cameras for a number of years, and those corrections are what I use. So far, they've been very accurate. My exposures with 8x10 usually run to between 10 and 30 minutes. I meter at 50 ISO.

One thing I have run into with these exposures: if the light changes during the exposure, it will have a very large effect, much greater than you might expect. I had one exposure with direct, late afternoon sun alternating with overcast as small clouds passed over. In the sun the exposure was about 10 minutes, and in the overcast more like 30. I had to watch the time and mentally integrate two exposure times. Kept me on my toes.
 

Kino

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Here's the table I use:

1s = 2s
2s = 7s
4s = 21s
8s = 59s
16s = Forget about it
32s = Forget about it
64s = Forget about it
128s = Forget about it
 
OP
OP

retina_restoration

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Kino said:
Here's the table I use:

1s = 2s
2s = 7s
4s = 21s
8s = 59s
16s = Forget about it
32s = Forget about it
64s = Forget about it
128s = Forget about it
Click to expand...

That's the same set of values I quoted in my opening post (and assuming from 16 seconds and up, your chart would still match mine) and those values gave me severely overexposed negs.
Note that I am not talking about pinhole work — I am using a lensed camera.
 

Kino

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Just trying to be humorous. Actually, I doubt I would try an exposure longer than 4 seconds on Fomapan/Arista EDU 100. I have MUCH better luck with Delta 100, but that is off-topic...

In any event, I have to ask if you reduce development time when applying the reciprocity adjustment?

Personally, I never have, but this table in "Photographic Materials and Processes" by Stroehel, Compton, Current and Zakia (1986) does recommend an adjustment (sorry for the crappy phone capture):

 
OP
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retina_restoration

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Kino said:
Just trying to be humorous. Actually, I doubt I would try an exposure longer than 4 seconds on Fomapan/Arista EDU 100. I have MUCH better luck with Delta 100, but that is off-topic..
Click to expand...
Oh, I see, yes. Sorry, I didn't get that it was in jest — I assumed it reflected your actual experience with the film!
 

FotoD

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Haven't done much long exposure with the 100 film. But Fomapan 200 works very well with Fomas times, at least up to 60min exposures (calculated).


These times look similar to what the OP has been using, so they probably won't help him much.
 

FotoD

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Some of Fomas films are quite red sensitive. I guess that could make a significant difference when making long esposures, if the meter is less sensitive to red light.
 
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