FP4 and HP5: ISO values and development times in DD-X.
Thanks to some advice from Thomas Bertilsson on another thread, Iíve started investigating the relationship between film ISO values and development times. Up to now Iíve been using HP5 film (box speed 400) and DD-X developer. I thought Iíd branch out into FP4 (box speed 125) so as to have an alternative film.
Iíve read in various sources that HP5 can be exposed at 400, 260 and 160 (according to light conditions and required shadow detail) and development times can be reduced accordingly. I assumed that similar arrangements applied to FP4. Now hereís the interesting thing: both the packing of FP4 and the info supplied with DD-X show that FP4 can indeed be exposed at ISO 50 as well as 125. On the other hand neither the packing of HP5 nor the DD-X info show dev times for HP5 exposed below the box speed (although adjusted times are given for higher ratings up to 3200).
This leads me to the following questions:
a. For HP5 lots of experienced photographers have worked out satisfactory exposure/dev combinations for ISO values lower than the box speed. Has Ilford got any particular reason for not mentioning these?
b. Ilford mentions only an approximate halving of the ISO for FP-4 from 125 to 50. Can one take it a further step lower to e.g. 32 as well (analogous to going down to 160 for HP5)? If not, why not?
ISO film speed testing is done following rigorous parameters. It yields one film speed for that set of variables (exposure, developer, agitation, temp, contrast index, etc.).
Different developers and other variables yield different working E.I.s. The largest of these is contrast index adjustments to adapt to the subject brightness range (the entire reason for the Zone System, BTZS, etc.).
The relationship between development time and effective E.I. is well-known. Generally speaking, less development results in a lower E.I. For example, I rate my film differently for each Zone System scheme (e.g., N+1 has a higher E.I. than N). I generally just use exposure adjustments to do this, but the result is the same: different E.I. for different development times for the same film in the same developer.
If you have a contrasty scene and need to reduce development time to compensate, then your E.I. will be lower, assuming the developer is the same. The opposite is true if you need to develop longer to increase contrast. This is what Ilford et al. are talking about when they mention using different E.I.s for different lighting conditions.
No film manufacturer is going to do a lot of testing with other developers and give you the entire spectrum of film speed/development time possibilities. We photographers need to do those tests ourselves. However, some give a little. Ilford gives "starting point" suggestions. If I'm not mistaken, Kodak supplies contrast index curves for different development times in their film data sheets. Of course, it will likely not be for DDX.
Theoretically, the relationship between E.I. and film speed is a function of time and a continuous change. You should be able to make a few tests at a few developing times and plot the results on a graph.
I find HP5 to be one of the most malleable films ever made. Ilford probably takes it for granted, which is why they probably don't go to great lengths discussing it. Sites like the Massive Dev Chart lists a wide range of combinations. I actually really like shooting it at ISO 1600 (pushing two stops), and developing it in undiluted D-76. This is my favourite shot at this film speed to date, for reference:
Twice Bitten, not shy
Ilford HP5 (4x5in), pushed to ISO 1600 in D-76, printed in the darkroom on 12x16in Ilford MG IV multigrade paper
My opinion: Precise timings and variances posted on internet websites are not all that useful, as it's unlikely that your circumstances and needs match that which is referred to. It's almost impossible to screw up an HP5 negative (especially through overexposure) so just go ahead and experiment. Experimenting in a format that doesn't come in little canisters enough to take 36 photographs on does make it easier, that's for sure.
P.S. There are no problems in shooting Ilford FP4 at ISO32, other than somewhat low contrast. When you bump this contrast up in printing, you get lots of grain. I much prefer to shoot Pan F at ISO32 instead, which is simply stunning in all aspects of image rendition to my eyes - here is an example (also a scanned print):
DD-X is a speed increasing developer and most use it as so. This may be the reason why Ilford does not recommend DD-X for pulling HP5 below box speed. I know many have gotten beautiful results pulling HP5 in high contrast conditions using Perceptol. FP4 and HP5 in 120 are my two main films and I develop them in ID-11 1:1. FP4 shot at 100 when spot metering, or 64 using in camera metering. And HP5 shot at 250 in camera with high contrast and 640 in camera with low contrast then increased development time. You need to run tests to determine your optimum development time for each film and developer. I wouldn't get too caught up in determining development times for each EI. There should be one EI and development time for FP4 in normal contrast and then another for N+1, N-1.. etc if you wish. Same for HP5. If shooting with in camera metering your EI's will be lower than if you shoot with spot meter using the zone system. This is the reason why many times different photographers have extremely different EI's for a single film. Some using spot metering, some use in camera metering.
You should read a bit about controlling film contrast. You can search around for explanations for the Zone System, but a quick look at the characteristic curves supplied in the Kodak Tri-X technical publication will be illuminating. If you go to page 11 you will see how changing the time in developer changes the slope of the characteristic curve. Overly simplified, changing exposure moves your picture up and down and individual curve while changing developing time/temperature/agitation will change the slope of the curve. There are plenty of good books that can be had for easy to follow explanations.
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Thanks for the replies. The point about the difference between spot metering and in camera metering is interesting and one which I had never heard before. I use a spot meter for meterless cameras and tend to rely on the camera meter in other cases unless there are critical questions of contrast. I'll do some intensive reading.
Philo: those are remarkably beautiful and accomplished images.