"True film speed" vs just developing the film more?

[IanBarber]

For those of us who don't have access to densitometers what's the easiest way to determine the true speed of the film we are using.

[Larry Gebhardt]

For those of us who don't have access to densitometers what's the easiest way to determine the true speed of the film we are using.

First determine your development time experimentally by printing, focusing on a mid grade paper like grade 2. If the contrast looks correct in the mid tones and highlights (ignore the shadows) you are there. If it's low contrast add 10%, and if it's too high subtract 10%. You should be using a normal contrast scene for this. Once your time is determined shoot the same scene at different film speeds. Pick a scene with normal contrast range and one that has details in the shadows. Outdoors I find most landscape scenes with trees or shrubs work well. I usually go box speed - 1.3 stops to box speed + .3 stops. For example FP4 is box 125, so shoot a sheet at 50, 64, 80, 100, 125, 160. Then develop at the time you determined earlier. Evaluate your negatives and choose the one that has recorded the shadow detail and isn't showing major blank areas. I find the best way is to print them and adjust the exposure time for your mid tones and keeping the contrast at grade 2. Each will require slightly different times. Pick the one with full detail with the fastest speed - that is your speed.

My results usually come out in the range of developing 10% less than the Xtol times and with a speed of -1 to -2/3 of a stop. Since I like slightly more open shadows I round down.

[IanBarber]

First determine your development time experimentally by printing, focusing on a mid grade paper like grade 2. If the contrast looks correct in the mid tones and highlights (ignore the shadows) you are there. If it's low contrast add 10%, and if it's too high subtract 10%. You should be using a normal contrast scene for this. Once your time is determined shoot the same scene at different film speeds. Pick a scene with normal contrast range and one that has details in the shadows. Outdoors I find most landscape scenes with trees or shrubs work well. I usually go box speed - 1.3 stops to box speed + .3 stops. For example FP4 is box 125, so shoot a sheet at 50, 64, 80, 100, 125, 160. Then develop at the time you determined earlier. Evaluate your negatives and choose the one that has recorded the shadow detail and isn't showing major blank areas. I find the best way is to print them and adjust the exposure time for your mid tones and keeping the contrast at grade 2. Each will require slightly different times. Pick the one with full detail with the fastest speed - that is your speed.

My results usually come out in the range of developing 10% less than the Xtol times and with a speed of -1 to -2/3 of a stop. Since I like slightly more open shadows I round down.

Thanks Larry, I shall try that and see how the results turn out

[Pere Casals]

For those of us who don't have access to densitometers what's the easiest way to determine the true speed of the film we are using.

Adding to what Larry pointed, You have a densitometer, just scan raw your negative alongside a ($7) Stouffer T2115 density wedge, you can check what grey intrevals are in an step of the Stouffer.

Also when you expose a test scene you may writte down how underexposed are your different shadows, just use the spot meter of a DSLR/SLR for example. Then with the Scanner+Stouffer densitometer you find what shadows have 0.1D over Fog+Base (unexposed film areas, interframe separation or example). Those areas in +0.1D are in the "m" speed point, so underexposed 3.3 stops from "true speed".

So correct for the "true speed" you were guessing. If you had the meter at ISO 100 but shadows at +0.1D were metered -2.3D only... then you have to correct the true speed by 1 full stop, if you use ISO 50 then those shadows with +0.1D density would instead have been metered 3.3 underexposed, which is the right setting for the true speed.

Just: when your true speed is correct then -3.3 stop shadows have 0.1D density over base+fog (fog+base = not exposed negative areas). If not, correct your "true speed".

If you want your exposure calculations based in "true speed" then you have to target -3.3 at +0.1D.

You can perfectly use any personal speed, but... what advantage has using true speeds ?

If you use always true speeds you will have a way more consistent metering across a range of different films/processings, if not with every film/processing you need a different rule wich is overcomed by using a "personal speed" (EI) for each film/processing, also not bad.

Absolutely this is a personal choice, some people like a more technical approach and some people prefer a practical way and going forward. Both kinds of people may make great art or nothing worth. The way you meter is not related to the work quality. For example AA was very technical and a great artist, but Karsh developed by inspection, and also he was a great artist.

Some people listen a soprano while watching the spectral domain to "see" the voice ormanentation. They may be sick or they may understand better the voice, this is what we are debating about film speed

[Doremus Scudder]

For those of us who don't have access to densitometers what's the easiest way to determine the true speed of the film we are using.

Go back and read my post, Ian!

[Drew Wiley]

Here's one of the main flaws in all this "real film speed" talk : You're measuring it based upon a threshold value above fbf. Well, airplanes also have their own kind of fbf taking off and clearing the runway. But they don't all take the same angle of trajectory to get to cruising altitude. "Straight line" films have one kind of trajectory; long-toe films, another; many films are somewhere in between. Lith film is almost like a helicopter that can go straight up once it is started. All of this affects your very definition of film speed. No cut-and-dried generic formula can do that. And all of these can be somewhat modified by development regimen.

[Pere Casals]

Here's one of the main flaws...

The flaw is not explaining how true film speed is calculated...

This is a number, tell me, how do we caculate it?

[Drew Wiley]

Why bother if it doesn't describe how gradation is actually rendered? Don't we all tend to take advertised box speed, maybe cut in half, then slowly work our way up to find what is appropriate to our own needs? But all the major manufacturers have tech sheets or web pages with their own densitometer curves relative to recommended developers or times. That should give a clue where to start, along with other people's experience.

[Pere Casals]

Why bother if it doesn't describe how gradation is actually rendered?

Of course with some try/error cycles we may solve it !!! We use a personal EI that accounts for our metering style, and that's all... I fully agree...

Anyway with the true speed calculation for a film/processing we also find:

> The Contrast Index and a good guess for the paper grade. We have the gradation.

> Exactly what shadows will be lost and what shadows will be damaged in the scene, from spot metering.

> What highlight latitude we have and what footprint in the glares. (we have the curve, so the shoulder shape)

> The toe and shoulder shapes also tells what we'll find in the printing process, if we are experimented in handling graphs.


Graphs in Datasheets are useful, specially those from kodak, if we use a processing described in the kodak graphs then we only need to understand how the graphs can be used in practice, amazingly not many photographers are able to translate an spot metering in the scene to lux·second in the graphs, me I've learned that recently.
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OP: "True film speed" vs just developing the film more?

This has an easy answer:

"True film speed" has a 3.3 stops latitude in the shadows, while "just developing the film more" increases contrast but it does not substiantally allow to record deeper shadows beyond what a the regular development time with same developer would obtain.

So if a "true speed" ISO 100 TMX is exposed at EI 400 then we won't have the regular 3.3 latitude in the shadows, but only 1.3 stops from the meter point if metering at EI 400, or a bit more from some small effect of the overdevelopment in the true speed.


"Developing the film more" essentially increases contrast, making an underexposed negative more printable, without improving much the "true speed" for the shadows.

[Bill Burk]

Pere, you know when you write 3.3 that you are rounding, right? It’s ok with me if you write that way if you occasionally acknowledge you are rounding for expedience but that it’s truly 3 1/3