finding film speed?

[David A. Goldfarb]

Not all developers develop thin areas and dense areas of the negative at the same rate. In addition, the rate at which dense areas are developed with respect to the rate at which thin areas are developed can be controlled by agitation. Think of the principle behind stand development (no agitation, long dev. time) to reduce contrast--the developer molecules that are adjacent to dense (highlight) areas are quickly exhausted, while the developer molecules in the thin (shadow) areas continue to act, bringing the shadows up and holding the highlights back to bring a neg of a contrasty scene into printable range. Now if a developer, by virtue of its chemical formula, can allow Zone I density reach 0.1 over base + fog density faster than another developer formula without letting the highlights getting out of hand, then it can produce a real film speed increase while maintaining normal contrast. Developers like Acufine, Diafine, and others act this way.



You don't really need to worry about this though, for what you're doing. You just need to know the film speed that results from your particular developer/film combination.

[Robert C. McColloch]

Picker is THE simple answer on how to determine personal film speed. A densitometer is NOT needed.

[Brian Ellis]

I second the suggestion to read Picker's book. A few quibbles with what's been posted so far. I wouldn't use a white wall, in theory it shouldn't matter but I think it's best to avoid the extremes when testing so I wouldn't use white or black. Also many walls are textured and you want whatever you're photographing to be smooth, not textured. I've used a gray card several times, also have used the smooth side of a cardboard box (with no writing on it of course). For your first exposure try to select a shutter speed that will allow you to stop down four stops at each of the film speeds you'll be trying without having to change the shutter speed in the middle of the tests. Also, you need to plan it all out ahead of time and do a few dry runs first because you usually have to move fast because the light has a tendency to change if you spend much time doing the tests and if that happens the test is no good, the light has to be exactly the same for all the different film speeds you try.

It isn't absolutely necessary to have a densitometer but it sure does help. If you don't have access to a densitometer I'd suggest letting The View Camera Store do the exposure and development times testing for you. I've used them several times and have been very pleased. You get much more information than you're likely to obtain on your own and the cost is only about $30, not much more than you'll likely spend on film by the time you finish with both the film speed and development times testing plus you'll have saved a lot of time and aggravation. The thing that finally drove me to stop doing it myself was when I kept getting a different base plus fog readings when doing my development tests than I was getting when doing the film speed tests. Between that and the changing light I think I went through a box of film trying to do the final series of tests that I did on my own and was never confident that I got it right.

[Jorge Gasteazoro]

:-) seems nobody is really answering your question so I will give it a shot.

A developer does not change the exposure index (EI) of the film. It mostly has to do with the way the film speed tests are done under ISO standards. For example Kodak, Ilford etc, have labs where all their instruments are calibrated under ISO, that is light intensity, metering, thermometers, timers, agitations times, agitation machines etc, etc. When they conduct a film speed test under these tight conditions they obtain a specific film speed.

Now then we come to you and your darkroom, you have a thermometer which I am sure is not calibrated, you have a meter which might, or might not be calibrated to ISO standards, etc. When you do your test all these factors add up to give you a different film speed, there is nothing wrong with this if the negatives you are getting are what you are looking for and you can consistently obtain these result. So this could be one reason for a different film speed.

OTOH perhaps you have heard of changing the EI when you do expansion (develop the film for longer time) or contraction (develop the film for shorter time) this has nothing to do with the developer being more or less energetic or changing the speed of the film, it simply has to do with the inherent contrast of the film. When you do a contraction, you have a scene which has a high contrast, and you are trying to "fit" all those tones in the film. Now when you develop, the developer has little effect on the shadows or "thin" parts of the film, no matter how much more you leave the film in the developer this parts of the negative will stay essentially the same, but do vary a little bit. So then when you are trying to fit a high contrast scene into the film if you develop for less time then those thin parts of the negative are more affected than the rest so you have to give them more exposure to counteract the lesser development time. In essence you are adjusting the contrast of the film.The easiest way to do this is to change the EI to a smaller number. The opposite also holds true for more development, since you are going to put the negative in the developer for longer time, you want the shadows not to overdevelop so give the film less exposure. This is done by changing the EI to a higher number.

These two are the reasons why YOUR film speed and the manufacturer's film speed are different.

If you really want to learn how to do testing correctly buy and read the BTZS book. It is a hard read, but the methodology once you get the hang of it is far simpler than the zone system.

As to the Picker book I am in the opposite camp, easier is not always better and in the case of the "minimum time for maximum black" test I find this a flawed test which does not really offer good information. If you want to learn how to make black prints, then use it, otherwise use a better method.

[Rob_3836]

"As to the Picker book I am in the opposite camp, easier is not always better and in the case of the "minimum time for maximum black" test I find this a flawed test which does not really offer good information."

I would like to hear some elaboration on this point.

Why is the minimum time for maximum black test flawed?

[Jorge Gasteazoro]

I would like to hear some elaboration on this point.

Why is the minimum time for maximum black test flawed?



IMO Rob it is a matter of percentages. Regardless of how careful you are when developing there are always small variations that take place. So for example, sometimes your b+f can be 0.08, sometimes it can be 0.11, a difference of 0.03 is no big deal unless you are doing your printing test based on a density of 0.1 over b+f. Then a difference of 0.03 is about 30% of the exposure. To me this is unacceptable. I have always said that a "standard" printing time should be based on a Zone V negative. You take a Zone V neg and make a print that has the same tone of the gray card. This has a few advantages:



1. Most manufacturers have grades 1, 2 and 3 with pretty close speeds, if you make your standard printing time based on Zone V then this printing time will apply to all these grades, or at least it will be so close that for all practical purposes you have an accurate first reference. Not so for the max black test, you have to test printing time for each grade. BTW I have verified this and done it as well as plot the curves, it is not something I am speculating about.



2. As stated before a difference in b+f of 0.03 can be as much as 30% of the exposure when using 0.1, the same difference when using a negative that has a density of 0.65 is about 0.5%, for all practical purposes this difference is insignificant.



3. A standard printing time based on a Zone V neg will apply with the same paper to most developer film combinations you might wish to try, thus giving you useful information. Again this is due to the percentage error, even if you have a variation in b+f as high as .05 or .08, this is still a small percentage of error that can easily be adjusted, not so with the max black test, if you change film or developer you have to do the test all over again, even if you are using the same paper.



So as you see, making the standard printing time based on a zone V negative gives you plenty of useful information. You can see how your print varies if you change contrast, you can easily adjust the time to a different film/developer combination and you avoid or minimize processing variations, these qualities are not present in the max black test, and of course all this without a densitometer.



Personally I hate testing, this is why I strived to learn how to do it right from the beginning, so I just have to do it once with repeatable, accurate results. IMO recommending Picker's method to a beginner is leading them down the wrong path.

[Mark_3632]

Brian

In terms of time available to me, and cost of materials, plus I do not have a densitometer 30$ sounds very affordable. I looked at the View Camera Store web site and cannot find the information. Of course I will contact them about it but I want a bit more info from you if you do not mind. What all did you need to send them and what was the turn around like.

William Great, one more variable to figure out. Hmmm... ---------------------------------- Damn it. I just want to go shooting. all of this thinking hurts. Anyone know of an autoeverything 5x7

[phil sweeney]

Mark, I think you should read the negative. But you do not need to do all that and I would not recommend doing all that stuff through the view camera store. I have used the zone system with good results. 0.1 over fb+f works for most films and developers but as Jorge points out there are problems. I have used a zone board for HC110, PMK, ABC and pyrocatHD (its just one method!). Those tests, result in a good speed for each except pyrocat. The zone board indicates at 0.1 over fb+f a speed 1/2 needed for pyrocat (i.e., overexposed). All photographers should be able to figure a "normal" speed with 3 negatives (and proof) and a developing time with 3 more. Most important one should be able to visually analyze a negative and see if the shadow densities are correct as others have stated! I have not used bergger film but if you are going to do pt/pd etc maybe you plan on using pyrocat. Great developer, good speed and probably for the bergger would rate at 200. I recently proved a speed for photowarehouse film in pyrocat with 1 negative. Its rated 125 and having experience with pyrocat I knew it should do well at the rating. I cheated using development by inspection.

[Rob_3836]

Jorge-

You do have some valid and interesting points regarding printing time being based on a zone V negative.

However, I do question your contention regarding the variances in fb+f readings. It appears that you are basing this on the allegation that "Regardless of how careful you are when developing there are always small variations that take place". While I have no doubt that small differences can take place, I would certainly think that these variances would be insignificant if you are careful to use the exact same temp., developer dilution, development time and agitation regime.

If this is done, I would be VERY surprised to see any significant differences in the fb+f readings. If there are, there is a problem with consistency in the development method somewhere in the chain.

When I did my testing, I did it with two unexposed sheets of film, each developed seperately (but consistenly). They both had the same fb+f reading.

Was this not the case for you?

[Jorge Gasteazoro]

If this is done, I would be VERY surprised to see any significant differences in the fb+f readings

This is exactly my point, what is significant?, and in relation to what?



I use a staining developer with many different times to adjust the CI, or G bar as we call it, and with this a variation in b+f is normal. Before I used Tmx RS and there was little if any change, but as I said, a .01 change is 10% of the exposure in your test. Also, two sheets do not a make a comprehensive sample, are you sure every time you make a neg this is your result? A proper testing procedure should always provide you with repeatable information and minimize the possibility of error where they can occur. Also, if you do contraction or expansion of the film to fit your paper you will get a different b+f regardless of how careful you are it is just the behavior of film, if you develop you film for 5 more min to increase your contrast, you will increase your b+f and once again the max black test is prone to a high degree of error.
Look, lets say you are correct and every time you develop a sheet of film you obtain 0.08 b+f regardless of development time etc, I am willing to accept this. Tell me then, what other information can you gather from your test? Can you change paper contrast and get useful information about the negative? Can you change film/developer combo and obtain useful information about the behavior of the film without a densitometer? You cannot with the max black test, but you can with the way I propose you do it.
I always thought that a test is designed to provide you with useful information under a wide range of circumstances. I find amusing that those who propose the max black test they do so because they "hate testing" yet they find themselves repeating this test more often than those who do it right from the start. If you have settled in a film/developer combo (which BTW is what I recommend to people who are starting until they have mastered it) then this is not a problem, you do your test and move on, but if you ever want to try anything new...well then as Reagan used to say "there you go again". :-))



Look, in the end I am not trying to prove that Picker is wrong and I am right, if you like the max black test then stick with it, some people with many years of experience like Steve Simmons swear by this test. IMO it is not a good test but that is only my opinion.