Linearity of pulling film and developer temperature

[cerber0s]

Two questions in one Is there a rule of thumb for how much to adjust the time when pulling film? Is the relation between developing time and developer temperature linear?

Yesterday I developed a roll of Fomapan 400 in Adox XT-3 (XTOL). The datasheet said 7 minutes at 20 degrees, my developer had a temperature of 22.5 degrees. The datasheet for Fomapan 400 gave 7 minutes at 20 degrees, and 2 minutes at 30 degrees. I interpolated and it turned out fine, but just to double check: Is the relationship linear?

Next I’d like to shoot the Fomapan 400 at 200, but can’t find times for it. Is there a rule of thumb for calculating how much I should decrease the developing time? Especially if I’m already adjusting for different temperatures.

 

[koraks]

Is the relation between developing time and developer temperature linear?

No, it's exponential in principle, but the curve shape is inconsistent, dependent on the materials used and even for the pure exponential part it will vary with film/dev combination.

Here's a chart based on C41 developer time/temperature data Rollei used to include with their Digibase kits:

Chart taken from here: https://www.lomography.com/magazine/236651-tutorial-rollei-c41-digibase-color-film-development
I made a similar chart once based on the same data but did a curve fit so I could easily interpolate time/temperature combinations.

Mind you, in the case of color development different time/temp combinations aren't perfectly equivalent since there will be differences in the rate of development in the different layers. For B&W, this is likely not a problem, although non-linearities do exist as I alluded to above. The further you stray from the regular 20-24C temperatures, the more unpredictable it all gets.

Case in point, I was being lazy the other day with some HP5+ in rather warm instant mytol, so I adjusted the time based on the convenient calculator on the Massive Dev Chart site - and ended up with horribly underdeveloped negatives. They're just printable, but only just. I guess the compensation formula just didn't hold for that particular film, developer and temperature combination. This is the compensation chart you get if you plug in some different temperatures for a recommended time of 10 minutes at 20C:

Note also how weirdly non-linear the horizontal axis on the Ilford compensation chart is; this doesn't look anything like the neat exponential assumption made in the Massive Dev Chart calculator:

I don't know about the film pulling question. I'd be inclined to subtract 15-20% or so per stop. That's what I've done with C41 on occasion and it seemed to be close enough. I suppose that here, too, things will break down if you take it too far; i.e. it'll work fine for 1 stop, maybe 2, but beyond that, all bets are off.

 

[cerber0s]

No, it's exponential in principle, but the curve shape is inconsistent, dependent on the materials used and even for the pure exponential part it will vary with film/dev combination.

Here's a chart based on C41 developer time/temperature data Rollei used to include with their Digibase kits:
View attachment 378967
Chart taken from here: https://www.lomography.com/magazine/236651-tutorial-rollei-c41-digibase-color-film-development
I made a similar chart once based on the same data but did a curve fit so I could easily interpolate time/temperature combinations.

Mind you, in the case of color development different time/temp combinations aren't perfectly equivalent since there will be differences in the rate of development in the different layers. For B&W, this is likely not a problem, although non-linearities do exist as I alluded to above. The further you stray from the regular 20-24C temperatures, the more unpredictable it all gets.

Case in point, I was being lazy the other day with some HP5+ in rather warm instant mytol, so I adjusted the time based on the convenient calculator on the Massive Dev Chart site - and ended up with horribly underdeveloped negatives. They're just printable, but only just. I guess the compensation formula just didn't hold for that particular film, developer and temperature combination. This is the compensation chart you get if you plug in some different temperatures for a recommended time of 10 minutes at 20C:
View attachment 378969

Note also how weirdly non-linear the horizontal axis on the Ilford compensation chart is; this doesn't look anything like the neat exponential assumption made in the Massive Dev Chart calculator:
View attachment 378968

I don't know about the film pulling question. I'd be inclined to subtract 15-20% or so per stop. That's what I've done with C41 on occasion and it seemed to be close enough. I suppose that here, too, things will break down if you take it too far; i.e. it'll work fine for 1 stop, maybe 2, but beyond that, all bets are off.

Excellent answer! Thank you

 

[loccdor]

Speaking generally, aren't most physics non-linear? Gravity, temperature, light brightness equations I believe are all exponential.

The equations that are linear are regarding geometry with objects made of straight lines (as you would expect), distance calculations, and time (when relativity is a small enough factor to be ignored).

Dilution vs. time, in many developers, seems to be pretty close to linear. I.e. half the developer strength, double the development. Though I think this breaks down at the extreme ends of the graph.

 

[koraks]

Speaking generally, aren't most physics non-linear?

I don't think I can quite get behind that statement because it's a bit opaque, meaning-wise. I do agree that exponential effects are common, especially in relation to human senses: sound and light we do indeed perceive linearly if the absolute power levels increase exponentially. There's of course a clear benefit to this in terms of the tradeoff between range and accuracy.

 

[loccdor]

I don't think I can quite get behind that statement because it's a bit opaque, meaning-wise. I do agree that exponential effects are common, especially in relation to human senses: sound and light we do indeed perceive linearly if the absolute power levels increase exponentially. There's of course a clear benefit to this in terms of the tradeoff between range and accuracy.

Yep. I was thinking about it a little more and it's because non-linear relationships usually have a surface area (squared) or volume (cubed) factor in their processes. Since we live in a world more abundant of 3-dimensional objects which sometimes have 2-dimensional approximated surfaces, more than we live in a world of 1-dimensional points. But that brings us back to the mathematical definition of linear (x to the first power), so I think I may just be stating the obvious and going in a loop of thought.

With film's flat 2d surface, or light going through an aperture/shutter which is a flat 2d plane, it makes sense that you would see a lot of "x squared" exponential math. Anyway, I think I'm getting off-topic.

 

[MattKing]

While the relationships may not be linear, in what we are mostly doing with black and white materials, a linear interpolation is probably going to serve well enough in the vast majority of cases.

 

[Doremus Scudder]

Koraks' answer is definitive.

A possibly easier reference is the Ilford time/temperature compensation chart found here: https://www.google.com/url?sa=t&sou...QQFnoECBUQAQ&usg=AOvVaw28z9G_BEEGBVcIDnTqV6xZ

It should apply to all black-and-white films closely. Keep in mind that some developing agents lose activity if the temperature is too low and, on the upper end, emulsion softens and flakes off if the temp is too high.

As for "pulling": If you rate your film slower you're simply giving it more exposure, presumably to get more shadow detail. With normal-contrast scenes, you would simply develop normally, i.e., no change from your standard time. However, if you're trying to deal with a very high-contrast situation, then you need to reduce development. How much really depends on the contrast of the scene, but 15%-20% less development is a good starting point.

FWIW, the downrating of film in high-contrast situations coupled with a reduced development time, which gets labeled as "pulling," is simply a way of ensuring good shadow detail in a situation where your in-camera meter will tend to underexpose and a reduced development time to tame the high contrast of the scene. We Zone System users call that a contraction development.

Best,

Doremus

 

[cerber0s]

Koraks' answer is definitive.

A possibly easier reference is the Ilford time/temperature compensation chart found here: https://www.google.com/url?sa=t&sou...QQFnoECBUQAQ&usg=AOvVaw28z9G_BEEGBVcIDnTqV6xZ

It should apply to all black-and-white films closely. Keep in mind that some developing agents lose activity if the temperature is too low and, on the upper end, emulsion softens and flakes off if the temp is too high.

As for "pulling": If you rate your film slower you're simply giving it more exposure, presumably to get more shadow detail. With normal-contrast scenes, you would simply develop normally, i.e., no change from your standard time. However, if you're trying to deal with a very high-contrast situation, then you need to reduce development. How much really depends on the contrast of the scene, but 15%-20% less development is a good starting point.

FWIW, the downrating of film in high-contrast situations coupled with a reduced development time, which gets labeled as "pulling," is simply a way of ensuring good shadow detail in a situation where your in-camera meter will tend to underexpose and a reduced development time to tame the high contrast of the scene. We Zone System users call that a contraction development.

Best,

Doremus

That’s a great chart, thank you!

 

[albireo]

Next I’d like to shoot the Fomapan 400 at 200, but can’t find times for it.

If you're using stock, you could use the official times in the manufacturer's data sheet for Fomadon Excel at 20 degrees. Here they are - page two, first column, third row

https://www.foma.cz/en/fomapan-400

Normally, you would aim for a desired target gamma, but you seem to need a specific EI. So do as I sketched below, but in the opposite direction:

So pick a target ISO from the vertical axis on the left. Trace a horizontal line towards the top curve (S curve). When your line meets the curve, trace a vertical line going down, to meet the Gamma curve and the X coordinate.

The value you'll read on the vertical right axis will be your gamma value. The value you'll find on the X coordinate will be the development time needed.

E.g at 20 degrees Celsius you can see that with Excel stock you'll be getting a g~.5 if you expose at 200EI and develop for 5 minutes.

 

[cerber0s]

If you're using stock, you could use the official times in the manufacturer's data sheet for Fomadon Excel at 20 degrees. Here they are - page two, first column, third row

https://www.foma.cz/en/fomapan-400

Normally, you would aim for a desired target gamma, but you seem to need a specific EI. So do as I sketched below, but in the opposite direction:

So pick a target ISO from the vertical axis on the left. Trace a horizontal line towards the top curve (S curve). When your line meets the curve, trace a vertical line going down, to meet the Gamma curve and the X coordinate.

The value you'll read on the vertical right axis will be your gamma value. The value you'll find on the X coordinate will be the development time needed.

E.g at 20 degrees Celsius you can see that with Excel stock you'll be getting a g~.5 if you expose at 200EI and develop for 5 minutes.

Cool! Thank you!

 

[DREW WILEY]

Part of the complication is that the activity of certain ingredients in a developer formula might respond to significant temp change differently than other ingredients. I've found that to be particularly the case with hydroquinone. Therefore, if you want to explore the consistency of linearity based upon a time change per se, it's best to stick to a single standardized temperature.

 

[cerber0s]

Part of the complication is that the activity of certain ingredients in a developer formula might respond to significant temp change differently than other ingredients. I've found that to be particularly the case with hydroquinone. Therefore, if you want to explore the consistency of linearity based upon a time change per se, it's best to stick to a single standardized temperature.

I’m not really set out to explore the differences , I just want to develop my films without failing

When I use one shot developers I always mix them with tap water to get them to 20 degrees. But lately I’ve been using replenished XT-3, which means that I have to work with whatever the room temperature is (18-24 degrees). I know I can cool it down, but I’m too lazy.

Kodak and Ilford usually have excellent graphs for temperature compensation, Foma do not.

 

[cliveh]

As others have pointed out the Ilford time/temperature chart is very useful. In my darkroom I have a small laminated card taken from this chart showing time/temperature for 3 degrees either side of 68F and never deviate to wider or lesser temperatures than this.

 

[Doremus Scudder]

The question arises: For what specific reason are you deciding to rate an ISO 400-speed film at E.I. 200?

If you have a good reason, fine, but if not, what is making you deviate from box speed?

If you just overexpose your film a stop for no good reason, you'll likely get a good enough negative to print, but there is absolutely no reason to find a development time specific to that overexposure. "Normal" contrast scenes need "normal" development, regardless of small overexposure.

The idea of "pulling," as I mentioned earlier, is a rather slap-dash general rule for dealing with contrasty scenes and in-camera meters that tend to underexpose such scenes. More careful practitioners, with spot meters and/or other ways to evaluate subject contrast and find optimum exposure for the shadows rarely, if ever, use the term "pulling."

Best,

Doremus

 

[cerber0s]

The question arises: For what specific reason are you deciding to rate an ISO 400-speed film at E.I. 200?

If you have a good reason, fine, but if not, what is making you deviate from box speed?

If you just overexpose your film a stop for no good reason, you'll likely get a good enough negative to print, but there is absolutely no reason to find a development time specific to that overexposure. "Normal" contrast scenes need "normal" development, regardless of small overexposure.

The idea of "pulling," as I mentioned earlier, is a rather slap-dash general rule for dealing with contrasty scenes and in-camera meters that tend to underexpose such scenes. More careful practitioners, with spot meters and/or other ways to evaluate subject contrast and find optimum exposure for the shadows rarely, if ever, use the term "pulling."

Best,

Doremus

I think that Fomapan 400 is actually an ISO 200 film. I’ve shot maybe 30 rolls of it, most at box speed, a few above as an experiment. I’m rarely happy with the results when I compare it to other films, but I’ve seen photos from other people using the same film where I really like it.

 

[albireo]

I think that Fomapan 400 is actually an ISO 200 film.

Sorry - this statement makes very little sense, doesn't matter how many times you read it on Reddit.

Did you study and understand the Foma graphs I posted earlier? They're pretty good, and they work.

 

[albireo]

When I use one shot developers I always mix them with tap water to get them to 20 degrees. But lately I’ve been using replenished XT-3, which means that I have to work with whatever the room temperature is (18-24 degrees).

Just use 1+1 one shot and cool down the developer portion via the water portion. Discard after use.

Any perceived or imagined advantages you are getting by doing replenishment over 1:1 will be brutally offset by the consistency and accuracy you'll achieve by using 1:1 with strict and reproducible temperature control.

 

[cerber0s]

Sorry - this statement makes no sense, doesn't matter how many times you read it on Reddit.

Did you study and understand the Foma graphs I posted earlier? They're pretty good, and they work.

Yes, thanks! No need to be sorry, I say lots of things that don't make any sense. I try not to repeat them though

I almost get it. I get how I find my developing time from selecting an EI, but you have me curious about the rest of the graph.

What do the gamma values tell us, are they in relation to something? Gamma 0.4 would be a very dense negative that would produce a very bright print? Would gamma 0 be completely black with zero transparency? Does gamma 1.0 have any special significance? Why do the curves flatten out at ISO 320, is it actually an ISO 320 film?

 

[npl]

OP is using Adox XT-3, a Xtol clone. Here's the relevant chart from the fomapan 400 datasheet :

I personnaly shoot F400 at EI 250 when using Xtol and use the normal developement time and it works fine. Should be OK at EI 200 to just stick with the normal dev time (7min stock), but as always it depend on the light, how the scene was metered, personnal tastes in contrast, and so on...

Boxes can lie, sometimes.

 

[albireo]

Yes, thanks! No need to be sorry, I say lots of things that don't make any sense. I try not to repeat them though

I almost get it. I get how I find my developing time from selecting an EI, but you have me curious about the rest of the graph.

What do the gamma values tell us, are they in relation to something? Gamma 0.4 would be a very dense negative that would produce a very bright print? Would gamma 0 be completely black with zero transparency? Does gamma 1.0 have any special significance? Why do the curves flatten out at ISO 320, is it actually an ISO 320 film?

Apologies - I'm travelling and have limited connectivity. Will reply later. Though I see npl is also helping with this. Thanks!

 

[cerber0s]

OP is using Adox XT-3, a Xtol clone. Here's the relevant chart from the fomapan 400 datasheet :

View attachment 379135

I personnaly shoot F400 at EI 250 when using Xtol and use the normal developement time and it works fine. Should be OK at EI 200 to just stick with the normal dev time (7min stock), but as always it depend on the light, how the scene was metered, personnal tastes in contrast, and so on...

Boxes can lie, sometimes.

Thank you!

Apologies - I'm travelling and have limited connectivity. Will reply later. Though I see npl is also helping with this. Thanks!

Thanks! If I was in a hurry I'd be shooting digital ;P

 

[Paul Verizzo]

Two questions in one Is there a rule of thumb for how much to adjust the time when pulling film? Is the relation between developing time and developer temperature linear?

Yesterday I developed a roll of Fomapan 400 in Adox XT-3 (XTOL). The datasheet said 7 minutes at 20 degrees, my developer had a temperature of 22.5 degrees. The datasheet for Fomapan 400 gave 7 minutes at 20 degrees, and 2 minutes at 30 degrees. I interpolated and it turned out fine, but just to double check: Is the relationship linear?

Next I’d like to shoot the Fomapan 400 at 200, but can’t find times for it. Is there a rule of thumb for calculating how much I should decrease the developing time? Especially if I’m already adjusting for different temperatures.

If you look at the Kodak Darkroom Data Guide and it's rotary calculator for time/temp for a given film and developer, it is linear on the circular dial. Same separation per degree.

Certainly possible that outside of the range in the guide, a process might become non-linear compared to those temperatures.

 

[Doremus Scudder]

I think that Fomapan 400 is actually an ISO 200 film. I’ve shot maybe 30 rolls of it, most at box speed, a few above as an experiment. I’m rarely happy with the results when I compare it to other films, but I’ve seen photos from other people using the same film where I really like it.

Realize that you are not "pulling" film when you think you are using it at its proper speed, even if that is different than box speed. Most good black-and-white photographers arrive at a personal E.I. (Exposure Index = personal film speed) that works best for them. The E.I. of a film can be different from ISO speed for a number of reasons, but mostly because of metering techniques and choice of developer.

So, if for you Fomapan 400 works best at E.I. 200, then just find a good standard development time that allows you to print negatives from both contrasty and flat scenes well using the contrast controls available to you int he darkroom.

Best,

Doremus