[CristiC]

On the original post, about "box speed" versus "real speed", I think that relates to the so-called exposure index, or EI. That refers to a speed rating (you do your own rating) assigned to a particular film and shooting situation. The speed rating is different than the film's actual speed, which is measured in a scientific way, according to a standard, ISO 6:1993 (Photography — Black-and-white pictorial still camera negative film/process systems — Determination of ISO speed).

There are reasons (mentioned earlier in this thread) such as the benefits of a large exposure latitude, shadow detail, personal preference about the results when developed in a way recommended by the film manufacturer. There are other reasons for film speed rating as well, such as compensation for a (particular) inaccurate camera metering system, or a miscalibrated camera shutter that consistently overexposes or underexposes the film.

In short, actual film speed is measured according to a standard, whereas the rated film speed is what you do to compensate, in order to get consistent results, according to your own preferences.

That is why there are tables of development times listed for EI, Exposure index values (that are in variance of the "box speed"). Btw, box speed is a third buzzword - it may be just a marketing label intended to lure customers to a certain use-case, as with ILFORD Delta 3200 Professional and Kodak T-MAX P3200. Similar to that saying: "the right way, the wrong way, and the Army way", in our dictionary of terms I would associate actual film speed with right (correct) way, the rated film speed with an (intentionally) wrong way and the box speed with the third option that is just a marketing label for the masses of buyers, although it is a tried-and-tested recipe to get somewhere in the ballpark of pleasant results.

I found the wikipedia article on film speed well done, (see also the article on sensitometry) and the many references at the bottom of that page comprehensive enough.

[DonV]

I don't believe film "speed" can be established without knowing the developer and development method(time/temp).

Given some "standard" developer and conditions, various films will have a particular "speed" ; but that speed will vary lot to lot due to quality control.

I think this is what CristiC said above- just in fewer words. JMHO.

[CristiC]

I don't believe film "speed" can be established without knowing the developer and development method(time/temp). Given some "standard" developer and conditions, various films will have a particular "speed"

Well, that may be a small misunderstanding. Please correct me if I'm wrong. From a practical, everyone's perspective, you may start with:

1. a certain film that you expose to (some) light. How you expose it follows certain assumptions on film sensitivity. You may overexpose / underexpose, or you may expose just right. The dosage of light is an assumption.
2. a certain developer (the chemicals) recommended by the film's manufacturer and using a certain dilution;
3. a development procedure that is precise enough regarding time, temperature and agitation, in a way recommended by the film's manufacturer in the product sheet. (Beware, some recommend more than one way!)

You may consider that a baseline (your baseline) and you get consistent results every time, when you follow that. Compared to this baseline, you then consider an alternative way to expose (overexpose/underexpose), in tandem with an alternative way to develop, thus following a recipe for push or pull processing. It is push or pull relative to your standard recipe - but do not mistake this to be the scientific standard on film sensitivity!

The standard, ISO 6:1993 (or the former german national standard "DIN 4512-1, Ausgabe Mai 1993") doesn't make assumptions on the development process. Just the film, the light and the exposure.

When talking about "film speed" or "box speed" or "actual film speed" or "rated film speed" or "exposure index" I want to establish a domain-specific-language, a dictionary of terms, so that everyone is on the same page. My point is that the "actual film speed" refers to how sensitive the film is, in compliance to a scientific method of precisely measuring the sensitivity at exposure, without considering the later procedures of development, what chemicals and time/temperature to use!

(further reading for german language users: film test - I thought that to be a valuable bookmark, saying that there is no "standard" development for negative black and white films)

but that speed will vary lot to lot due to quality control.

Possibly, but maybe not that much. How the film stock is stored over time at the producer, at the logistics company, at the seller and finally in your care, until used (possibly years later), that may have a bigger impact than QC. (ref: cool & dry)

[photoptimist]

As a statistical two-step analog process (exposure + development), film really has no true "native' or "real" speed.

There really is no lower-bound light level that leaves zero grains "exposed." Even in near pitch darkness, some photons hit the film and some grains form sensitivity specks. A sufficiently aggressive developer and long development time will bring out a latent image of the few grains that were hit by a few photons.

There really is no upper-bound light level that creates 100% saturation of 100% of the grains. Even in blinding bright light, any variation in light level means the grains have variations in photochemical effects. A sufficiently mild developer and short development time will leave the least-exposed grains less developed than the more-exposed grains. (see https://en.wikipedia.org/wiki/Latent_image for an example of a usable latent image exposed 24 stops or 4 trillion X over "box speed"!)

That said, some speeds are better than others. But which speeds depend on which definition of better. Like every exposure-related decision in photography, the choice of ISO/ASA setting for a given emulsion and the choice of development parameters comes with trade-offs in speed, grain, contrast, latitude, and response uniformity. Even the official ISO 6:1993 definition of "film speed" involves some arbitrary choices that may not be "best" for all photographic scenarios.

Negative films don't have a sweet spot, they have a sweet region that lets the photographer push or pull the film. For high speed films (for which the photographer naturally prefers a faster film), it not surprising that the film's parameters and development conditions bias the outcome relative to the arbitrary standard.

Thus one of the fun (sometimes frustrating) aspects of film photography is the opportunity to play with film speed, development chemistry, dilution, and time in hopes of getting a better final result.

P.S. the ISO definition of film speed does define a particular developer scenario (one that creates a specific increase in above-fog-level film density over a specific increase in exposure). That ISO standard development process may not be optimal for film speed, grain, latitude, contrast, or anything other than setting a standard. Thus, the "standard" for film speed really is not the best or correct speed of the film, only the one that fits the arbitrary technical definition of the standard.

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Last edited by photoptimist; 01-03-2022 at 01:26 PM.

[tuco]

Do you know if say two people claiming different speed of a paticual film are using the same developer, agitation profile and are using a densitometer to conduct their speed tests? Leaf shutter leneses are also big varialbes in establishing a working speed.

[CristiC]

(...) In several articles and posts I've read, the suggestion is to shoot at "real" speed rather than the box speed... but no-one ever mentions if the development times change. I assume they don't.

Here is a funny example of development time that doesn't change, no matter what film speed rating you choose: the process is called "stand development" with Rodinal. Some people may regard that a "standard" development procedure. That is a very personal standard to each and everyone, which they love to tweak and twist to extremes such as many hours / overnight development in the fridge or to a "semi-stand development" lasting maybe half an hour, then some agitation, then rest again for another 30 minutes or so.

Development time is typically one full hour every time, while not caring at all about "real speed" / "box speed" / "any speed". Forget about overexposure, underexposure, film type, room temperature, agitation. Just leave the can to sit there, one hour.
Then you may get a somewhat flat negative (with less contrast) that is intended for digital scanning and later digital tweaking and printing. This is an example that works well with lower speed films with regard to film grain.

How it works: highlight areas develop faster than areas of shadow. Developer around the highlights stops working after a certain time and then the remaining time lets the shadow detail develop further. If you don’t agitate the film and stand for one hour the highlight detail and shadow detail both have time to develop. The highlight detail is not blown, as the developer becomes exhausted around highlight detail sooner, so it stops. (Link here)

[JohnMc]

There were may pebbles in Siddhartha's path. Learn to do snip tests. A roll of 36exp can yield 2 - 6 good usable snips from which can can start walking your path to enlightenment or/and enlargement. The best or right combination is what puts on paper or screen what you sought, what you saw, what you want to see. There are ample combinations that will render that gray card well while moving the black or white. If you take your roll and shoot two sets of 5 exp brackets rated at 200, 400, 800 using your meter and then process them using the same developer at different dilutions or times, or even different developers altogether you will begin to see and understand better even if you only view them on a light table (though a proper enlarged contact sheet is best - it is possible to scan so long as you can keep the same settings for the whole series locked).

[filmmaster]

The problem is, there are issues that arrise depending on what developer is used.

I once sent in 12 rolls of black and white film, various speeds, various brands, various emulsions. MANY came back funny looking, some were almost transluscent...

When i complained, i discovered the company doing it used 1 developer for ALL black and white film, That seemed completely reasonable and logical.

But they also used the same LENGTH OF DEVELOPMENT for all black and white film..

go look at the mass dev chart and tell me how many developers let you process kentmere 100 the same time and method as Kodak Tri-x or even Foma 400

[JohnMc]

That's not really a developer issue so much as it is an operators error.

[DonV]

I expect filmmaster's experience is more the norm for "mass market" development- very little or no customization or realization of film differences.
Now if you send it to a special lab- you may get some attention to your film or requests.

And today, there is little or no "mass market" for film processing; so what one gets depends on the individual lab and their policies.

All of which is why I prefer "digital", it removes a plethora of variables- not to mention cost. JMHO.

[BigMackCam]

Folks, thank you for all the responses thus far. Seems I opened something of a "Pandora's Box" I'm reading all the responses with interest and appreciate your input

I prefer "digital", it removes a plethora of variables- not to mention cost. JMHO.

I love digital, but I'm really enjoying film thus far. It's a real challenge and there's so much to learn. I can't say that I prefer one over the other... they're so very different, both the process and the results. The variables in film are both perplexing and fascinating, and the lack of certainty and predictability compared to digital (at least, based on the limited experience I have thus far) is really refreshing to me. I feel incredibly fortunate to have both

[DonV]

Folks, thank you for all the responses thus far. Seems I opened something of a "Pandora's Box" I'm reading all the responses with interest and appreciate your input



I love digital, but I'm really enjoying film thus far. It's a real challenge and there's so much to learn. I can't say that I prefer one over the other... they're so very different, both the process and the results. The variables in film are both perplexing and fascinating, and the lack of certainty and predictability compared to digital (at least, based on the limited experience I have thus far) is really refreshing to me. I feel incredibly fortunate to have both

Yes,
I had enough "fun" with film in the '60s and "70s and '80s ! All you say is true and why I have no desire to go "back" to those good old days when there was no other option.

[filmmaster]

I expect filmmaster's experience is more the norm for "mass market" development- very little or no customization or realization of film differences.
Now if you send it to a special lab- you may get some attention to your film or requests.

And today, there is little or no "mass market" for film processing; so what one gets depends on the individual lab and their policies.

All of which is why I prefer "digital", it removes a plethora of variables- not to mention cost. JMHO.

There were a few places that used the same actual lab to do the processing.... but the better labs FORCE you to get things you dont want like over priced prints.

[CristiC]

I've read quite a lot about many films having a box speed that's arguably higher than the "real" speed... for instance, ISO 400 films that are allegedly closer to 320, 250 or even 200 in reality. In several articles and posts I've read, the suggestion is to shoot at "real" speed rather than the box speed... but no-one ever mentions if the development times change. I assume they don't. So, if I shoot Fomapan 400 at, say, ISO 250 - 320 (as many would suggest) and therefore technically over-exposing it with reference to box speed, do I keep the development as per the Massive Dev Chart timings for ISO 400?

To the original post I'd like to clarify some aspects:

While the general recommendation "to expose for shadows" or to somewhat overexpose film (on principle) is valid for both negative BW films and for negative color films, that is a more of a hint than a rule and it relates to the broad exposure latitude of negative film. Positive film (slide film) doesn't have that much wiggle room. But because Mike mentioned Fomapan 400, let's assume negative black and white film for subsequent considerations.

Most people used to send their film to a specialized lab for development. Nowadays, and more specifically when using negative black and white films, I reckon that most people enjoy to develop that kind of film at home and thus begin to experiment and more precisely steer towards a desired result, through control of development parameters, as compared to a more uniform or "standardized way" pursued by labs, which doesn't fit everyone's preference all the time. Whereas color film is processed with C41 process /chemicals, the same way all over the world, negative BW film allows for a wide range of different chemicals and processes. There is no standard.

The analog process has two parts: exposure and development. Let's ignore part 3, darkroom printing. Assuming that the exposure was "done the right way" for a given "film speed" - may that be the "box speed" or your own rating for film speed (aka the exposure index) and not aiming for push- or pull- processing, let's see what you can do at home to properly develop the film. Proper means: according to a personal preference for density, contrast or acutance, based on tales that you read or you were told, as a starting point.
It has nothing to do with standards, definitions, "real speed" or the absolute truth .

Variation of development time ( +/- deviation from an established recipe - such as the one that you get from Massive Dev Chart) leads to modified contrast levels, if other parameters are kept as in the recipe.
Let's consider an example from the Ilford HP5+ datasheet:

Note. Development times may need adjusting to suit individual processing systems and working practices. If an established system is producing good results, adjust the recommended development times until the desired contrast level is obtained.
Development times in other manufacturers’ developers are included for your convenience and are only a general guide.

On page 5 of that Ilford HP5+ datasheet is a graph, the characteristic curve - plotting the density versus the relative log exposure. Here is the characteristic curve of Fomapan 400 too. That is a hint of what to expect, if you do it right. Notice the 3 curves for 7min, 9min, 11min! Those are three curves, not just one! Guess what happens when you push or pull? You change development time. Just as if you would play with "film speed" at exposure, within certain limits.



Now to the exposure part. All of the above is assuming that you have set ISO/ASA 400 at your analog camera and this setting, along with the available light & scene, made your camera metering system to recommended a certain exposure, that is defined through a shutter speed and aperture.

But the exposure triangle has three parameters. You can change any of them in order to "overexpose" or "underexpose". The ASA 400 setting is not cast in stone! Before the actual exposure you can change the film speed rating for just that frame, to get "overexposure" or "underexposure", just as you would get on digital in TAv mode when turning the exposure compensation + or -, which affects the ISO setting, up or down.

You can expose the entire film at ASA 400 or you can get creative and expose particular frames at a "film speed rating" of your choice. Later, you develop the whole film as for ISO 400, to get desired density / contrast levels. Hence, my answer to the original question, on whether to adjust development times, based on a supposed "real speed" or not, is: definitely NOT, don't adjust development time for that reason.

[CristiC]

P.S. May I just leave these bookmarks here? About characteristic curves for film:

Kodak's Basic Photographic Sensitometry Workbook - a well made PDF <---- start here
A Practical Guide to Using Film Characteristic Curves - on another forum
Tom R. Halfhill's "Personalizing Your Film Speed" - I think JohnMc meant this, at post #22
and
comparing characteristic curves and the meaning of separation - on photo.net with this image: