Film Reciprocity Failure

Stegosaurus

Stegosaurus

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I am well aware of reciprocity failure of film and I'm accustomed to making adjustments when necessary in low light. However, I also indulge in a bit of pinhole photography. Unfortunately my latest attempt was marred by completely overestimating the exposure required. Which made me wonder....

Is there a practical difference in reciprocity failure adjusted exposure time in bright light with a small aperture (pinhole), compared to taking a long exposure picture in genuinely dim light using a large aperture assuming the theoretical EV of the two scenarios was the same?
 
Stegosaurus said:
I am well aware of reciprocity failure of film and I'm accustomed to making adjustments when necessary in low light. However, I also indulge in a bit of pinhole photography. Unfortunately my latest attempt was marred by completely overestimating the exposure required. Which made me wonder....

Is there a practical difference in reciprocity failure adjusted exposure time in bright light with a small aperture (pinhole), compared to taking a long exposure picture in genuinely dim light using a large aperture assuming the theoretical EV of the two scenarios was the same?
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I think the answer is no, given it's related to the emulsion response to the light over time.

As it happens, I've done some 'Dim' shots for FPOTY in the last week, waiting to see how my reciprocity calculations turned out!
 
The thing with pinholes is knowing the equivalent F-stop in the first place which IME takes some trial and error.
 
As far as I know, there should be no difference. The effect depends on the time, rather than how much light is involved, although with long exposures the reason for the long exposure is a small amount of light! As Sean said, in post #2.

The effect happens at the other end of the scale, with very short exposures whichs adds to my conviction that it's all about the time. The older high powered flashes that had very short exposure times needed to have allowences made. The usually quoted ranges of "safe" shutter speeds used to be 1/2 to 1/1000 second, but I haven't checked data sheets for a while, and not at the short end, as my exposure times are 1/500 at the briefest with the lenses I have, and working at f/16 or less with 125 ISO film I hardly need such short speeds.
 
You might find these useful:

Pinhole calculator (Web based app)

Exposure calculator (Android app)

Reciprocity app (Android app)

I am sure you can find suitable alternatives for Apple products.

I used them to work out exposures for my pinhole camera and they work really well. Find the F stop from the pinhole calculator - from that work out an exposure and then adjust it for reciprocity failure and Bob's your uncle. Worked a treat.
 
@Thmaga and @StephenM are correct. It's solely to do with the amount of light per unit time (or really, the total exposure) being outside of the reciprocal nature of the response of the film, and not to do with the conditions before the lens/pinhole itself.
 
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Jetstream Rider said:
You might find these useful:

Pinhole calculator (Web based app)

Exposure calculator (Android app)

Reciprocity app (Android app)

I am sure you can find suitable alternatives for Apple products.

I used them to work out exposures for my pinhole camera and they work really well. Find the F stop from the pinhole calculator - from that work out an exposure and then adjust it for reciprocity failure and Bob's your uncle. Worked a treat.
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Thanks for these. I actually thought I'd done the exposure calculation pretty much by the book. I have a little table of adjusted exposures made up for the film in question (Fomapan 100, known to suffer quite badly from RF) and I used an android app as a light meter on location. I've used the app with my Bessa, so I know it's been in the right ball park and the table has served me well previously. I was photographing in bright winter sunshine and I thought at the time that the exposure time seemed a bit generous (4 minutes), given the sun. I double checked but same answer. So I was a bit peeved when I got a very dark negative.
 
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My only thoughts on that are that the pinhole may be bigger than you think - if you drill a hole with a drill it could easily be bigger than the drill, depending on how you did it. Also, is the hole one with sharp edges? A rounded hole may let in more light than you think. The other thing is, is the pinhole just too big? The nice thing about the app I linked to is that it takes account of different film stock. It used to use 2 different processes to do that, one as set by the manufacturer and one theoretical based on a scientific model. I don't think it gives both of those anymore, but the key point was that there are different ways of taking reciprocity into account - so maybe your table is just a little off, or uses a method with assumptions that didn't work in your case?
 
Thanks for all your thoughts. After a bit of digging, I am now thinking that not only was the image overexposed, it is also badly underdeveloped. Or fogged. I used HC-110 at dilution H. I've read that this developer is not a good match for Fomapan 100 but it's all I had to hand. And it's getting a bit old. Rodinal next time!
 
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Stegosaurus said:
I've read that this developer is not a good match for Fomapan 100
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Nothing but peoples opion, you can only make a personal judgement by experimenting yourself.

FWIW I've only ever used 'B' solution but have to say that all the results that i have had using fomapan have been spot on .
If the negs have had faults, they haven't been due to HC-110, even from the last yorkshire tea coloured dregs of the bottle.

Rodinal??.....Might be OK but depending on film speed, I found it had a tendency to give grain the size of dinner plates.
 
Asha said:
Nothing but peoples opion, you can only make a personal judgement by experimenting yourself.

FWIW I've only ever used 'B' solution but have to say that all the results that i have had using fomapan have been spot on .
If the negs have had faults, they haven't been due to HC-110, even from the last yorkshire tea coloured dregs of the bottle.

Rodinal??.....Might be OK but depending on film speed, I found it had a tendency to give grain the size of dinner plates.
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Yes, I think I might have had better results using the B solution and I've certainly read it lives forever, but the doubts linger. However, the advice on the Fomapan 100 datasheet was not to use dilution B as the developing time was very short (3 mins). But the results with H have been disappointing. I haven't used Fomapan 100 much so I think some experimentation is due, if only to establish my film stock is ok. How do you develop it?

I actually like the results Rodinal gives, grain and all.
 
Rodinal is the developer I use, but I also only use medium and large format film, and never faster than 125 ISO. I've seen the extreme enlargements used to illustrate the comparative grain size and sharpness of Rodinal compared with (from memory) D76/ID11. That said, FP4 on 6x7 negatives was fine as far as I enlarged (A3/12x16).
 
Stegosaurus said:
the advice on the Fomapan 100 datasheet was not to use dilution B as the developing time was very short (3 mins)
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Stegosaurus said:
How do you develop it?
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MDC ( Massive Dev Chart) states Fomapan 100 in HC-110 B solution 6 mins ( I haven't read datasheet tbh but 3 mins not only sounds very short but also doesn't relate at all with the MDC recomendations.

I base my time on this 6 mins MINUS 15% to allow for constant agitaion in the orbital processor, so 5mins 6 secs @ 20C

I might add that I measure the developer using a 3ml egg spoon so the actual amount of concentrate in the developer solution is never going to be 100% accurate but I always get consistently decent results.
 
Asha said:
MDC ( Massive Dev Chart) states Fomapan 100 in HC-110 B solution 6 mins ( I haven't read datasheet tbh but 3 mins not only sounds very short but also doesn't relate at all with the MDC recomendations.

I base my time on this 6 mins MINUS 15% to allow for constant agitaion in the orbital processor, so 5mins 6 secs @ 20C

I might add that I measure the developer using a 3ml egg spoon so the actual amount of concentrate in the developer solution is never going to be 100% accurate but I always get consistently decent results.
Click to expand...

Thanks, that's very helpful and I shall try that. I measure out using a syringe, so I'm fairly confident it's reasonably accurate :-)
 
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