Fomapan 100 reciprocity: excessive.

[retina_restoration]

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]

@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.

 

[retina_restoration]

@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.

Glad to know it's not just me effing something up, thanks. I hope Ian has something to offer.

 

[koraks]

Do any of you know if there are updates to the Fomapan 100 reciprocity data that are more accurate?

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]

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.

There must be something to that.

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

 

[RalphLambrecht]

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.

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]

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

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]

This coefficient suggests fairly significant reciprocity failure

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?

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

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.