Hitting ASA Triangle Does Not Mean You Got Full Film Speed

[RalphLambrecht]

I get an EI of 200-250 for Tmax 400 in D761+1 as wqellbut why does that matter to you if you are satisfied with negs and results?if EI250 gives you all you needand has sufficient shadow detail, go for it.

 

[Stephen Benskin]

That thread shouldn't be titled "TMY is 250 speed", but "TMY in D-76 full strength is 250 speed". AFAIK box speed is no longer tied to a specific developer. There is a good chance that TMY will reach true ISO 400 speed in a more modern developer, or even D-76 1+3.

TMY is 250 speed based on what method. It's 400 based on the ISO standard. The reason the standard no longer has a specific developer is because of the T-Max films. Kodak used D-76 for the films during the design stage, but the T-grains didn't respond the same in the ISO developer. The standard changed in order to have a closer agreement with real world use. When the T-max films first came out, they had EIs and not an ISO.

 

[snapguy]

old school

I guess I am Old School. When I go to set my camera's exposure I wet a finger and hold it up. That tells me the f stop and shutter speed with b&w. I attended some of the Leitz company's coast-to-coast Leica Flying Short Courses and they tried to tell us that b&w negs should be exposed and developed so you could print them properly on number four single-graded paper. Anything less was overexposed. My wet finger technique works better and save a lot of time away from actually composing and shooting photos. Does that make me a bad person?

 

[Stephen Benskin]

Michael, by not stating the developer somewhere, Kodak isn't adhering to the standard and technical shouldn't be using the ISO prefix.

 

[Stephen Benskin]

When I was working in the photo lab industry back in the day, I had access to Dick Dickerson. He was the head of the B&W R&D department. I even spent the day with him and the head of the team that created the T-Max films and Xtol. They are the ones that told me the story about D-76 being the primary developer during the R&D of the T-Max films.

 

[Rudeofus]

From what I read here on APUG, all films to be released were tested for satisfactory results with D-76, because that was/is the most commonly used developer. "Full speed" is a property of an emulsion and a hard limit, therefore D-76 can't possibly give "full speed" if Microphen, TMAX, DD-X and Xtol give 1/2 - 2/3 stop more. As it just so happens, if you add 2/3 stop to ISO 250, you end up very close to ISO 400 ...

 

[Stephen Benskin]

Let's not forget that most people compare the ISO to the results from Zone System testing and the two testing methods aren't comparable. All things being equal, the Zone System test will almost universally yield a 1/2 to 1 stop slow EI than the ISO speed. This doesn't mean that the ISO speed is wrong. It means the test parameters are different.

 

[Rudeofus]

I'm not following. When you say "full speed", it sounds like you are defining it as "maximum emulsion speed", which is not implied by the ISO standards. There is likely a hard limit to maximum speed for a given emulsion (and of course we would need to define it), but for TMax 100 (just an arbitrary example), that might be considerably higher than its nominal or ISO speed.

A well formulated developer will give you "full emulsion speed". There are some special developers which yield a concave characteristic curve, and as a result can gain a tiny bit more shadow detail without letting contrast go through the roof, but the wiggle room is small. "Full emulsion speed" seems to refer to the maximum speed you can get with a good developer that gives a straight characteristic curve. Both D-76 and TMAX have such a straight characteristic curve, and if TMAX gives you 2/3 stops more than D-76, the latter can't possibly give you "full speed". Bill Burk's measurements seem to confirm this.

I assume when Kodak says D-76 yields full emulsion speed with a film - say TMax 100, that they mean you can get 100. And that other developers such as Microphen, XTOL etc. might give you slightly higher speeds.

The question is: when did Kodak state that? Did they make that statement before TMAX/Microphen/DD-X hit the market? Did they make that statement when the ISO speed definition mandated a specific developer?

In my opinion the term "full speed" would be meaningless if many developers can reach more.

 

[Rudeofus]

Crawley would tend to lean more in your direction, since he "felt" the true inherent speeds of films were higher than people were all used to at the time. This seems to be based mostly on the fact he was big into Phenidone, which tended to give small increases in properly balanced formulas, vs comparable MQ developers.

Note that all/most developers released by Kodak/Ilford/Fuji in the last couple of decades are based on Phenidone/Dimezone-S, too. That was not some fad pursued by Crawley alone.

In fact, given Stephen's in depth knowledge of speed methods, it might be interesting to look at some of the curves we generated with my experimental high speed/low gamma developers. You may recall at the time I tried to make the point to Alan that all we could really do is compare toe shapes and fixed density points to some reference (XTOL normal CI in my case). ISO, fractional gradient, etc. would all seem to fail in extreme cases like that, and quantification becomes problematic.

Normal developers are meant to be used more or less as the ISO speed definition requires, i.e. for normal contrast development. That's why this definition of film speed makes sense. You have seen yourself that if you force a film developer to lower contrast, you will sometimes shift the toe to the right (e.g. your Xtol N-x test), and sometimes not (e.g. your own LC devs). This means you'd have to use a modified version of ISO speed measurement for the contrast you are after, and possibly with a different number for how far the speed point lies above b+f.

 

[Bill Burk]

My original reason for starting this thread was the relative speed difference between two different films TMY2 and Panatomic-X which didn't jibe with their difference in ISO.

Now the surprise is that my 0.10 speed point shifted about 1/3 stop between two tests of the same batch of film 100 TMAX.

Only difference in my process was how much time elapsed since the developer was mixed

This is similar to Fred Aspen's case of a certain brand of distilled water killing his developer, except in my case this is not a dramatic drop in speed.

Another surprise is the development time is the same and the gradient is the same, 0.62 CI, in both cases and both meet the ASA triangle.

Yet the 0.10 speed point differs by 0.13 LogE units between the two. I have a tentative conclusion that the older developer did not attain as much speed as fresh developer.

We've established why I trust the EG&G sensitometer, so I don't believe the shift is an exposure difference.

If there isn't another explanation, I'll work under the assumption that the balance between the different developing agents and buffer changed over time. I guess it's time to start documenting my pH as I go.

 

[Bill Burk]

I get an EI of 200-250 for Tmax 400 in D76 1+1 as well but why does that matter to you if you are satisfied with negs and results? if EI250 gives you all you need and has sufficient shadow detail, go for it.

This thread documents how I calibrate my sensitometer, so it's important to know the film speed so I can work backwards to deduce the exposure. But that's theory. In practice you are right, it doesn't matter - because when I use EI 250 on my meter... my shadows have the detail I want.