Why is it that the development times and film speed supplied by the maufactures of film differ, sometimes by a lot, from the recommendations by photographers on this forum ? I would think that the Research and Development department of the film manufactures would get it right on the money. No?

Francis T. Knapik

-- Francis T. Knapik (inirolem@aol.com), October 10, 2001

Answers

There are a lot of variables in film processing that are out of the control of film manufacturers. When your thermometer says 68 degrees is it really 68 degrees or is it the same temperature as my thermometer that might read 72 degrees. When you mixed 50ml or stock solution with 450ml of water did you get it right? Or was it really 60ml and 440ml water? Are you pushing or pulling the film? That changes the speed of the film. Do you agitate 5 seconds every 30seconds or 5 every 60? How vigorously? There are many more variables that I'm sure will be added below, but I think you can see that there is no one answer.

RICARDO

-- r (ricardospanks1@yahoo.com), October 10, 2001.

As mentioned above, many variables in individual processing techniques, water quality, pH, meter sensitivity, shutter speed accuracy, shutter speed efficiency, etc. cause the individual variations.

Then, too, is the developer used for ISO tests can't be bought, and you probably wouldn't want to use it. And, I believe, their developing technique isn't anything commonly used. The developer & technique are chosen for laboratory repeatability, something very important in developing a standard, but less so for users (not that we can be sloppy).

Note that with the TMax films, Kodak chose to give EI (exposure index) numbers instead of ISO, probably trying to give users a better sense of true usable speed than meeting a standard.

Charlie

-- Charlie Strack (charlie_strack@sti.com), October 10, 2001.

The most probable cause of the mismatch between the given dev/ times (in the small useless sheets of paper that you find in the packaging of your film) and the optimal ones is the fact that most developers (espacially the fine-grain ones) reduce the nominal film speed in order to give the best results (in terms of grain, sharpness tonal range etc). The manufacturers don't want to oblige people to shoot their film in lower E.I.'s, this is quite a bad advertising for their films (hey, this Tmax 100 I just bought is not a real 100, it' a 64 !!!). So, they augment the developing time (in the expense of higher contrast, coarser grain and poor renditio of highlights) just to be able to keep the nominal speed of their film intact... Other reasons might be the incompatibility of printing sources (I print on a condenser enlarger, so I have to dev less my negs) and other details. Experiment and find your own times.

-- George Papantoniou (papanton@hol.gr), October 10, 2001.

I think George has hit the nail on the head. I would be bad marketing for a company to tell the public their film is EI 64 when the competition claims EI 100. So, as George states, they offer a development time that yields correct midtone densities at the inflated EI, thereby sacrificing shadow detail.

Take almost any nominally rated 100 speed film, cut it's EI to 64, reduce development by 25% from the recommended time, and you will see a marked improvment in overall image quality. And you will have a far easier negative to print, too. But don't expect Kodak, Fuji or Ilford to tell you this. Ask them and they'll tell you their film is indeed ISO 100. Period.

-- Ted Kaufman (writercrmp@aol.com), October 10, 2001.

Actually, the manufacturers exposure and developing times are right on the money. Provided you use very accurate equipment and have good water quality and agitate exactly the same as they do. The other point is that you have to like the look of "ISO Standards". In the "average" situation this should look good. Unfortunately, it seems most people don't shoot in average situations. ISO standards and all of the other standards that came before were designed to give consumers a way of comparing products from different manufacturers. The problem is that most photographers don't realize that what works best for them will have nothing to do with ISO standards. Kodak with T-Max has tried to deviate from the standard and tried to give better information and admit that their times and exposure information have nothing to do with ISO standards. It amazes me that some think this is just a marketing ploy. The answer to your question is that you really do need to test for exposure and for development using your own equipment to find out what works best for you. Have fun.

-- Jeff White (jeff@jeffsphotos.com), October 10, 2001.

I don't think there's anything sinister about the conservative (over-) development times that manufacturers provide in most developing tables. They are a standardized recommendation, and as with any craft it's up to you to optimize your materials and methods. Once you know whether your methods are on one side or the other of the "standard", you can interpret their tables to suit your personal technique. All that's necessary is that they obtain and report their data in a consistent way.

-- Tim Nelson (timothy.nelson@yale.edu), October 10, 2001.

Jeff and others have given very good explanations, but I'll add a little bit also.

I can't speak for other manufacturers, but at ILFORD we run development tests to give a Gbar of 0.62 (Gbar is a slope measurement, similar to but different from Contrast Index. The methods are different enough that there is no conversion method). This same contrast ratio is used for all developers, and the time that gives this contrast is what is published, rounded to the nearest 15 seconds. The testing used for developing times is not connected with the ISO testing for film speed. ISO measurements use exposures made by calibrated machines, and processed in very exacting conditions. These exposures and processing conditions bear little resemblance to most photographic situations; it is simply a standard that is easily replicated in the laboratory, regardless of where you are. ISO speeds of different brands of film are directly comparable, but only as far as the ISO standard goes. For your particular shooting style (including subjects, lighting conditions, and equipment), you may see variations between two different films having the same ISO speed rating.

On developing, there are a large number of variables. Different people will not only have different techniques, but also different ideas of what constitutes a "perfect" negative. Added to uncalibrated thermometers, graduates, etc., this can lead to vastly different optimal times. Quite often, people will comment to me about our developing times. Most of these people say that our times are "right own", and say they are better than the numbers other companies publish. But other customers will complain, saying that our times are too short or too long. I would guess that people vary as much as -30% to +100% from our published times.

So the bottom line is that published numbers are good to use for starting points for your testing. The good news is that as long as you stick with one manufacture's numbers, the difference will probably remain roughly constant.

David Carper ILFORD Technical Service

-- David Carper (david.carper@ilford.com), October 10, 2001.

More variables: condenser vs diffuse enlarger, lens flare, paper choice.

-- Tim Brown (brownt@flash.net), October 11, 2001.

I have to agree with what David (form Ilford) says, at least partly, because I have observed that the processing times given by Ilford are the closest to the ones I think as correct. This is mostly true for the other manufactuers films in their developers dev times (that Ilford has published in a very nice table a couple of years ago) and not so true for their own films (which they prefer to rate at higher E.I.)... Well, I should not be so mean, Ilford is OK, compared to other big film manufacturers. There. I was honest (and nice).

-- George Papantoniou (papanton@hol.gr), October 11, 2001.