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

Something has been bothering me a bit as of late - comments like "X film is a 400 ISO film but really it performs like a 200 ISO film". Example include Fomapan 400 (I've heard things like it is better at 200 or 320) or Pancro 400 (which to me in 4x5 tends to give me thinner negatives using stock times if I rate it at 400). I'm also confused at the notion of "full speed" developers - that feels like a function of development time to attain the rated speeds. It's a question irrespective of just erring on the side of over-exposing the film a bit or intentionally pushing and pulling film.

I guess stated another way I'm not sure the relationship in development times when developing at box speed. If I'm buying a 400 ISO film I kinda expect I should judge it, at least initially, by its box speed. So if my negatives are thin, I feel like I should add time until they are the density I'm looking for then then, if desired, I might push or pull?

Or stated a third way, what is the difference in shooting, say, Fomapan 400 at 200 over just developing it longer and expose it at the box speed? Why is one better than the other (if it is)?

Hopefully that makes sense. It's been bugging me a bit because while I like the look of Pancro 400 for instance, in the 400 range I tend to lean on speed a bit more, especially in 4x5. If I don't have to worry about speed, I tend to use TMX (which I know looks very different from Pancro). If I want to take photos of flowers and it is slightly windy for example, having to loose a stop of speed before dealing with filters and what not changes things. HP5 I feel like I know well enough to be comfortable with it at box speed and pushed (I've gone as far as 1600 in 4x5 but I suspect I could go to 3200 and get good results with my process).

This is a general question but for what it's worth I tend to use XTOL (1:1 though lately I'm experimenting with replenishment).

All developers will exhibit the same properties, but there is a standard developer they use to test for box speed. That said, the toe of a film curve (shadows) becomes non-linear at a certain point and will not develop more when development time is increased. That is effectively the box speed. You can develop more and the mid to higher part of the curve will increase, but the toe will always stay at that box speed.

Some developers have different levels for the toe, as such, they are called speed-increasing or speed-reduction developers.

Effective Index (or EI) is not the speed of the film, rather just what the user shot/developed the film at.

You seem to be confusing exposure and development. They control different things, but they do interact somewhat. Exposure controls shadow density on your negative film, while development controls highlight density.

A film's "box speed" is determined under laboratory conditions using a specific developer at specific times, temperatures, and agitation techniques. Since this is just about impossible to reproduce by any of us without the required laboratories, equipment, and controls, what it is, is a guide. A place to start.

What the Zone System (Adams and Archer) addresses is how to find your personal exposure index (PEI, or just EI), and your personal normal "N" development time for your preference of developer, time, temperature, and agitation style.

If you'll put in the work reading, understanding, and then testing, you'll end up with a system customized to your equipment and techniques that allows you to control both your shadow detail and highlight detail, accurately and (more importantly I think) repeatably.

If you don't like the Zone System, there are dozens of variants out there. There's likely a method that fits the way you want to work if you'll look for it.

BTW, there's really no such thing as "pushing" a film. Exposing the film less records less shadow detail which you can not recover in development. What you get from the increased development is mostly an increase in highlight density. This can make the film easier to print in the darkroom, and it's also responsible for the increase in "graininess" of the "pushed film". But if you look hard at the shadows in the print, you'll find them lacking shadow details. Because you underexposed the film. Pushing is more accurately described as "under exposure + over development".

Rule of thumb with B&W: over-exposing a stop is better than under-exposing. Due to variables in processing (and in my case inaccurate LF shutters), it's all revealed after processing. (My shutters are all a little slow. So am I. :) ) ... for processing I begin with the manufacturers' recommendation. I'm stuck in my ways and use only D-76 and Rodinal and leave exotic developers to my heroes on this forum.

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Originally Posted by m00dawg

So if my negatives are thin, I feel like I should add time until they are the density I'm looking for...

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Negatives being thin has nothing to do with EI. It's controlled entirely by development.

Shadow detail is a function of exposure and EI, and cannot be changed by development.
If information is not in the latent image, no amount of development can create it.

- Leigh

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Originally Posted by m00dawg

rated speeds.

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Read Beyond The Zone System book, ebay $4

Read this: https://en.wikipedia.org/wiki/Film_speed


Definition of speed:

Any film speed (with certain non ISO processing) tells you that film toe is at 3.3 stops underexposure from what an "standard" meter says, so with an spot meter you know what scene spots are in the linear part of the curve, or underexposed enough to be in the toe. It is important to understand this because this is absolutely basic.

This is becasue speed is useful: you know what scene spots will be in the toe and what spots will be "acceptably" captured because of being in the linear share.


Definition of ISO speed:

As always, if using D-76 (or equivalent in speed) and using recommended standard development time you have the toe at -3.3 from what meter recommends, but you also have the ISO standard contrast.


If a rated speed (with certain processing) don't places toe at -3.3 this is not a film speed, this is a way to say how you expose.


FOMA 400 is not a ISO 400 film, it is 400 (non ISO) speed if developed with an speed boosting developer, but it has lower ISO speed with D-76. Datasheet says that 400 speed can be reached, but they should mention with what developer.

If using a "speed" the toe is not at -3.3 then this is not a film speed, but a way to say how one exposes.

All these posts regarding nuances are largely distractions.

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Originally Posted by Jac@stafford.net

All these posts regarding nuances are largely distractions.

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Jac, no distraction, the speed term is used around very bad, IMHO.

In the massive development chart (with some errors) and in datasheets we have development of TMX to obtain 50, 100, 200 and 400. Only the 100 is a ISO speed. The 50, 200 and 400 are non ISO EI because contast is not standard, and film toe may not be at -3.3 stops, one thing is pushing and another one is modifying film speed.

When someone says "I rate TMX at xxx speed" he usually says nothing about film speed, if he has calibrated his process then may be he is talking about film speeds, if not he speaks about his film usage.

WOW this was a ton of good info in a really short time. Thank you thank you thank you everyone! Great things to think about. I've working my way through The Negative right now but it's a dense book and I may need to re-read it hehe. It sounds like the specific piece of the puzzle I was missing was the relationship between the toe and the box speed. That didn't click until now.

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Originally Posted by m00dawg

WOW this was a ton of good info in a really short time. Thank you thank you thank you everyone! Great things to think about. I've working my way through The Negative right now but it's a dense book and I may need to re-read it hehe. It sounds like the specific piece of the puzzle I was missing was the relationship between the toe and the box speed. That didn't click until now.

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Let me insist, read Beyond The Zone System, a flawless explanation about how the thing works.

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Originally Posted by Pere Casals

In the massive development chart (with some errors) .

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With very many errors. The Massive Development data is deficient in two regards: first it accepts user experiences which, in my opinion are ill founded, full of poor practices and second: many charts are simple numeric extrapolations, and we should know that is a wrong way.

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Originally Posted by Pere Casals

Let me insist, read Beyond The Zone System, a flawless explanation about how the thing works.

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Ooops I thought you meant the Zone System as covered in The Negative. Noted! Took a peak at the preview and TOC on Amazon and yes this looks quite fantastic for the subject at hand (latest revision was updated in 2013 as well!?). Added to my list of must-have books, thanks!

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Originally Posted by Jac@stafford.net

With very many errors. The Massive Development data is deficient in two regards: first it accepts user experiences which, in my opinion are ill founded, full of poor practices and second: many charts are simple numeric extrapolations, and we should know that is a wrong way.

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Ok... don't consider the Development Chart, let me correct my statement: just see recommended developments in the TMX datasheet for diverse speeds:

> 100 speed is ISO, it is for sure that the toe is at -3.3 stops with recommended standard processing, and it delivers standard contrast.

> 200, 400, 800 EI are film Exposure Index, non ISO, and not speeds. With the recommended development by kodak the toe may not be at -3.3 so it isn't with a new speed, but a way to make a printable negative. For this reason the say EI and not Speed:

Attachment 186477



> Somebody saying he rates TMX ISO 80, this is not a film speed if he made no calibration, this is how he shots... , this is also for sure.

> Using a high speed developer would modify the film speed, this is: it modifies the required exposure for a spot to be in the linear region and outside the toe.

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Originally Posted by Pere Casals

Let me insist, read Beyond The Zone System, a flawless explanation about how the thing works.

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If you follow Adams' recommendations in his book The Negative, and don't take all his disclaimers into consideration, you will make nothing worth printing. Ever see that photo of him dressed as Moses with the Ten Commandments done by his followers? The highlights are all blown out and the shadows are opaque because the negative was so thin they had to print on #4. At least Davis reveals in his complicated system that the effective speed of TRI-X developed in HC110 B for 5:00 at 68* is 64. Picker claimed some complete understanding of Adams' system and offered to give you your personal EI for $5 if you send him your test negative to measure. Adams hated Mortensen , probably because of all the beautiful women that posed for Mortensen, but his book "Mortensen on the Negative" shows you how to read a negative without a densitometer and make the appropriate adjustments.

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Originally Posted by Neal Chaves

Davis

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Yes... one thing is a recipe to get a working method and another one is BTZS. There are many good recipes out there, everyone is good if we make some personal adjusments for it.

But basicly BTZS is not a recipe, it's a compendium about technical sensitometry. It (primarily) not tells you how to expose/process, it tells what we'll obtain depending on how we expose, process and print.

With a calibration and a spot meter we can predict what particular density we'll obtain in the negative for an scene spot, and the same for the printing process. So it opens the scope of photographer's mentality.

BTZS is advanced knowledge that may not be necessary most of the times, but if we want to adjust (for example) a reversal processing it will save a lot of repetitive testing.

You know, all the information above is correct. It just seems to me that we often dump more information and techno-babble on to someone looking for a basic, halfway-easy-to-comprehend answer that we risk overwhelming them with detail.

Let me attempt a simpler, albeit less-detailed, reply directed at the OP's questions:

First, as mentioned above, standard ISA film speed is determined by lab testing with specific parameters for exposure, developer and amount of development.

In practice, any of these parameters can be different for us.
1. If we use a different developer, it might not give the same film speed as the lab standard. This happens all the time. Differences are in the range of one-stop slower to a bit faster (the extremes being attainable only with more specialized developers). For example, HC-110, according to Kodak, will give an E.I. about a third of a stop slower than ISO standard.
2. We more than likely all meter differently than the lab standard, whatever type of metering we use. This affects where the low values get placed on the film. We may have to add more exposure for our way of metering to get the shadow detail we like.
3. We often don't like to develop as much as the ISO standard, usually to keep highlights from becoming difficult to print, etc. Changing development time has a small effect on film speed; less development = slower E.I. and vice-versa. We may need to adjust our E.I. to match our desired development time.
4. Finally, some smaller manufacturers don't rate their films so precisely to ISO standards, so they may be overstating their film speeds a bit. We need to test and adjust for that.

Yes, you should judge your film initially at published box speed and using the developer and developing time recommended by the manufacturer. But then, be aware that some of the above discrepancies will likely come into play and you'll have to make adjustments. If you don't feel like learning the Zone System or whatever right away, just follow Kodak's age-old advice: "If your negatives consistently have too little shadow detail, increase your exposure (i.e., slower E.I.). If your negatives are consistently too thin (i.e., underdeveloped so you don't get light enough highlights), then increase development time (and vice-versa)."

Keep in mind that exposure determines how much shadow detail is recorded on the film. This is a function of the built-in speed of the film and can't be changed very much by development; just by a little as mentioned above, and that usually on the slow side.

Development controls the contrast spread from the more-or-less fixed shadow details to the highlights. We can increase the contrast (difference in density on the negative) between low and high by increasing development and vice-versa. We fine tune our development time to find the best compromise for us. Zone System users have different development times for scenes with different contrasts, but many just find a good middle time and use the contrast controls available when printing to make up the difference (especially roll-film users who can't easily switch development times for different frames). The idea is to be in the middle of your adjustments for a "normal" situation so you have room on either side to deal with more or less contrasty scenes.

One comment about "pushing": As mentioned above, this is basically intentionally underexposing the film (i.e., losing shadow detail and placing the highlights somewhere on the usual mid-range of the negative) and over-developing (to get those muddy highlights up to where they should be!). This results in a printable negative with a lot of separation between tones and no detail in the darkest shadows. This is fine for many low-light situations where making the shot would have otherwise been impossible; it is even a "look" that people have learned to like and so gets used for "normal" situations as well. If you want full shadow detail, however, you need to make sure you have enough exposure. How much shadow detail is enough for you determines your E.I. for any particular situation.

Hope this helps,

Doremus

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Originally Posted by Doremus Scudder

Keep in mind that exposure determines how much shadow detail is recorded on the film. This is a function of the built-in speed of the film and can't be changed very much by development; just by a little as mentioned above, and that usually on the slow side.

Development controls the contrast spread from the more-or-less fixed shadow details to the highlights. We can increase the contrast (difference in density on the negative) between low and high by increasing development and vice-versa. We fine tune our development time to find the best compromise for us. Zone System users have different development times for scenes with different contrasts, but many just find a good middle time and use the contrast controls available when printing to make up the difference (especially roll-film users who can't easily switch development times for different frames). The idea is to be in the middle of your adjustments for a "normal" situation so you have room on either side to deal with more or less contrasty scenes.

Doremus

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Required shadow detail also determines the effective film speed because the low value densities (Zone I-III) are set largely by exposure with development having very little effect on them. As noted, if you don't get the information on the film, no amount of development is going to bring it out. Use the film speed that will give a Zone I density approximately 0.1 density unit over the film base plus fog (fb+f). Develop the film to give a Zone VII exposure a density reading of approximately 1.15 over the fb+f. This requires a densitometer, however and I think I've offered to ready anyone's negatives who sends them to me for the cost of a SASE (as long as it doesn't get out of hand which I doubt it will). Cheaper than Fred's $5 cost as Neal noted. For the same $5 you can buy a used copy of Picker's the Zone VI workshop, which is more readable and easier to understand than Adams' the Negative. Just PM me for the address if you want me to read your negatives.

I'll stay on the sidelines chuckling this time.

Thanks for the discussion folks! I ordered Beyond the Zone System as it seems like a great read but also learned quite a bit just right here. In regards to the offers to do density testing of films, it sounds like to do that I would need to shoot a gray card or a test card in expected lighting setups to get good data from that? I'm not sure I'm quite ready for that but I do think it's a worthy exercise.

For now I am still seeing that Pancro 400 seems to work better more at 200 given my meter, lens, and subject combinations so far. I get better shadow detail. Admittedly I'm not properly using the zone system in these cases and it's been in shade or artificial lighting. I suspect a bright sunny day with a very wide dynamic range will be different (from what I've read, Pancro 400 provides a bit more shadow detail than HP5 in this regard). I definitely like it, not sure if I like it more than HP5 yet though. I still need to do some portraits with it and more shooting in general, but will probably shoot it closer to 200 until I work my way through BTZS, The Negative, and am able to consider doing some testing.

I do agree with some of the sentiments that one can over-complicate this to the point all I'm doing is taking lab shots. I don't want to go that far, and I do have a tendency towards over complication :) But I think getting a better handle on negative exposure and evaluating things would be helpful. I'm not applying it particularly well but I do think I favor the zone system, at least when doing serious shooting in 4x5. For 35mm, I think just adopting a pull/push mentality tends to work better for me since the photos are more snapshots and tend to be taken with haste. HP5 at 800 tends to work well for me - I like the look and I get good negatives so I'm not too bothered by it. 4x5 is certainly another story - part of the reason I shoot it is because it's methodical and it stands to reason being more calculating about exposure makes a ton of sense to me.

You don't shoot a gray card, but work with either a transmission step tablet or reflection gray scale, containing a full range of gray values from black to white. This is then measured with a densitometer and plotted. All a gray card does is indicate "middle gray" (Zone V), which might or might not indicate the middle of the true film scale. Simple gray card readings work better in color photography.

Aha ok good to know. Do you still need to meter for that (since how you meter would be part of this equation?). Could be quite the combination if testing the meter, the lens, the film, and the lighting.

You are on track. With BTZS, I'd recommend you make the necessary effort understand every bit of knowledge in the first half. The logarithmic math is essential because it's all based on that. Don't think you will have to use all that theory in practice, but by understanding well sensitometry you will be aware of what you are doing in any situation.
____

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Originally Posted by m00dawg

Pancro 400 seems to work better more at 200

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Just acquire that knowledge, then you will know why 200 works better with the way you meter. With an spot metering you will know what density will have any that spot of the scene in the negative, if tonality is compressed there or not in that spot, and you will know what development require that sheet to craft the visualization you want, and if the negative will be easy to print. I encourage you to get that knowledge. Next step is to use that tool for aesthetics, this is the difficult part to me.

That level of control is not always necessary, but exposing a LF sheet may require a remarkable effort, so nailing things is essential. With rolls we bracket on a doubt, this may be cheaper than thinking, but a photographer like John Sexton does not bracket, he rather makes two shots with same settings to have a backup, and he does it because he has all under control.

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Originally Posted by Drew Wiley

I'll stay on the sidelines chuckling this time.

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A wise decision! :)

I'll chime in again, on the side of simplicity, and offer another approach.

I've managed to arrive at a high level of technical excellence when it comes to exposure and development without a densitometer or using higher math. Not that I can't do math or understand logarithms; I just don't need it to calibrate my film exposure and development.

My approach is strictly visual and based on making a "proper proof" on the printing paper I use most (which, unfortunately changes every year now, but I digress...).
Making a print with the minimum exposure to render the clear area (rebate) of the negative close to maximum black on the paper is the key. Make a print leaving a strip of the paper uncovered by the negative (contact print) or by leaving a bit of space beside the negative in the carrier (enlargement) that will receive more exposure than the area covered by the negative. Make a test strip, dry it down and inspect it in light that you consider optimum for displaying prints (this is critical; too bright and you'll end up underexposing and vice-versa). Find the minimum exposure that renders the black of the rebate almost indistinguishable from the black of the uncovered stripe. Note all your parameters (exposure time, f-stop, enlarger head height, etc., etc.). That's your "proper proofing time."

Now, simply make a proper proof of a typical negative on your favorite paper, choosing a medium grade (2-3, or whatever gets you in the middle of your contrast adjusting possibilities) and evaluate. If shadow detail is lacking, you need to expose more (change your E.I.). If it is way up on the scale, you're exposing more than you need to. If the highlights are dull and gray, you need to develop more; if they're blown out blank white, you're overdeveloping. Make adjustments, make some more negatives and proper proof them till you get the results you want. That's it.

You can refine the above for contractions and expansions, all the different films you use and all developers you use. Quick, easy, no investment in precision equipment (i.e., no densitometer), etc.

I'm now to the point that when in the field I indicate which paper grade I wish to print on along with my development scheme (N, N+ etc.). I'm right on 75% of the time and only off by a grade the rest of the time.

There are a lot more refinements you can make after this, but getting these basic things right right away makes your life a whole lot easier.

I love reading about sensitometry and tone reproduction and I think it helps me with the nuances and details of the whole process; I just don't need it to find the right exposure and development for my films...

Best,

Doremus

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Originally Posted by Doremus Scudder

I've managed to arrive at a high level of technical excellence when it comes to exposure and development without a densitometer or using higher math.

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The recipe you explain is really very good advice, and it's completely worth to follow, there is a lot of wisdom in it.

Using a recipe is perfectly fine, but if one knows well the theory then he also knows what the recipe is to work, when is to fail, and what to do insted.

Making a film calibration was a basic exercise in photography schools for very good resons.

About investment, my high precission Nuclear Associates (ex RX gear) was $20, or one can simply scan the Stouffer alongside the calibrations to compare with no additional cost. A lux meter is $15.

It's a personal choice, one may want to learn the theory or not, but by spending a weekend one may experiment a boost in his mentality. At leat one knows why is he doing what he is doing.

One can also buy a Calibrated Step Tablet, with each of the 21 steps already read on a densitometer and written down on the package. Then, for beginner purposes, one can do crude "visual densitometry". You take a sheet of opaque black cardboard and punch two small holes about 1/4" or less in diameter, several inches apart, using a paper punch or leather punch. The step tablet is ordinarily on a sheet of 4x5 film. You place the area you want to read in your own test negative under one hole, over a light box, then using the other hole, see which step on the official tablet most closely resembles the particular density on your own shot. I won't go into the whole procedure here, and only mention how you don't necessarily need to purchase an expensive densitometer just to get started.

Ah that's a good idea! I have a feeling in practice I'll be doing an amalgamation of all these, especially while I read the book - I don't plan on suspending all my photography until I figure all this out hehe.

On the tablets, something like this? They are more expensive than I thought so was curious if I'm looking in the wrong place (prices are similar on the usual sites).

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Originally Posted by m00dawg

On the tablets, something like this?

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No!!!!

http://www.stouffer.net/T2115spec.htm T2115, $7

Or the calibrated one $17, T2115C http://www.stouffer.net/Productlist.htm


You scan your negative alongside with the Stouffer and by comparing you have a densitometer !!! :)

Also soon I'll release this freeware: https://www.largeformatphotography.i...ation-software to make it easier.

You make the contact copies of the stouffer, you scan the stouffer and the copies, et voilà... you have the curves with a click. Just buy a $15 densitometer if you want absolute units for light, like in the kodak datasheets.

Oh haha that's MUCH BETTER!

Yes, thank you. There are indeed very expensive step tablets on glass used to calibrate densitometers etc themselves. But a basic Stouffer 21-step tablet on film should be around $40 or less. I suggest buying a new one. Old ones might turn up a lot cheaper, but also might have significantly yellowed over time, making them hard to use.

Agreed! Up to $40 seems worth it. Thanks so much Drew, and everyone! Learned a heckofalot and now have some homework to do :)

So I've been watching Ben Horne and Alan Brock's videos this morning while sipping my coffee. A thought occurred to me. Maybe I AM metering wrong. I recall reading in The Negative that lightmeters are calibrated to middle gray so that tends to be what I meter on. Sometimes I'll take the dark and light points, look at the range but also do an average and I'll usually set the shutter speed to that average.

That works - I get negatives, but I wonder if that's one reason why Pancro 400 seems slower. When I've shot it in 35mm I used on-camera metering for instance (though I recall those lightmeters, really any lightmeter, is tuned for middle-gray?).

Seems like I need to re-read that chapter. I'm having less issues with negative film but I've probably had more sheets of Velvia 50 exposed poorly than those exposed well (a few I felt I nailed though and I can understand why folks like Ben Horne pay so much money for 8x10 slide). I was conscious of the dynamic range but also still setting the shutter speed typically to the middle of the range, and I'm wondering if that's wrong (if I should be leaning on the highlights instead for slide and on the shadows for color negative).

That said, middle gray is meant to be Zone V? So as long as I'm within the dynamic range of the film I should, artistic license aside and expansion/contraction aside, have a well developed negative?

Sorry I know I'm kinda making things fly off the rails a bit with regards to the original question. And likewise it sounds like I need to do some (re)-reading as well :) But it was a thought I had this morning while checking out Ben's film reveal - absolutely stunning colors. He really knows how to use Velvia 50.

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Originally Posted by m00dawg

That said, middle gray is meant to be Zone V?

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First, what is middle gray ? Middle gray can be different things, see here the "Table of middle grays":

https://en.wikipedia.org/wiki/Middle_gray

But, yes... you identify in the scene what you want it to be the middle gray in the print and this is Z-V, so what the meter says +/-0. You may want to modify that, but this is the "Standard" way.

If using the "true speed" of the film to meter, those areas that are not underdeexposed beyond 3.3 stops will be in the linear zone, so with no compression in the tonality but, depending on the film, as you underexpose you may be having a quality loss, so you need to know how (with your film/process) areas at -1, -2, -3 and -4 will be. You may place what you want in Z-V instead in Z-VII, to record the shadows that would be lost, in that case you may develop a shorter time to not have too high densities from overexposed areas, this underdevelopment won't mess much in the shadows. Basicly this is the N+/- development: expose for the shadows but develop for the highlights.

You may also want a safety factor, a modern LF shutter when was sold new it had a +/-30% specs accuracy, so a 1/30 can be 1/20 or 1/40, so it can vary a full stop and still being in specs. With negatives better to have a little overexposure than having a loss in the shadows, with slides (velvia) you have to ensure that you don't overexpose, because in that case highlights are easily damaged.

The method explained by Doremus is perfectly good, my recommendation is that first study well the BTZS book and later follow what Doremus explained, then you will be ready to nail what you want. There is a point since you don't see the meter reading, but you are visualizing the densities in the negative without thinking much, and the way the print will look straight, and what you'll have to do to print your visualization from your negative.

After you reach that mental point you will be in control with little effort and you will be able to focus on what light does with subject. Something like riding a bicycle, when one has practice he is not thinking in how he has to move le legs to pedal, and he may look forward and travel. And of course you'll also know when you should make accurate meterings for a complex scene.

The important thing is that when you have a pitfall you understand what happened, and what you would do instead next time.

There Pere! That does indeed help clear things up (and give me for to think about and do as I should probably get around to timing my shutters...).

Well, no...just because you know what Zone 5 is, doesn't mean the specific film involved will span the actual scene contrast, because neither is a fixed number. It all depends. And there is simply no substitute for accurately measuring your shadow versus highlight endpoints when significant contrast is involved. There are all kinds of potential exposure models you can choose from, including those already mentioned. But any of these have to be implemented hand in hand with a lot of actual shooting, developing, and printing before it really becomes easy. But don't worry. The learning process is fun and rewarding too.

On another site, another discussion, a fellow we call Photo Engineer said a film’s true speed is the point of inflection, the point at which instruments are capable of detecting the departure of the characteristic curve from base plus fog.

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Originally Posted by Bill Burk

the point at which instruments are capable of detecting the departure of the characteristic curve from base plus fog.

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Bill, in fact this is the speed point, I guess, not the film speed.

But it's true that the film speed is calculated directly from the exposure in the speed point. (development also has to deliver the standard contrast to be the ISO speed.)

ISO standarizes the position of the speed point "m" as having 0.1D more density than unexposed areas (fog+base). The film speed instead is calculated from the exposure in the speed point to make an standard meter to aim x10 the exposure in the speed point, this is 3.3 stops.

Not sure that -3.3 stops works for reality. If I meter/place textured shadows (dark moss on underside of wet rock, shadowed underside of fallen tree) on zone 2-ish I get no texture. Zones 3-4 give better texture and shadow separation. I set the f-stop and shutter accordingly and keep my EI of 100 constant for FP4+. So in theory I should have a film speed closer to 50 for my processing style if I read all this stuff correctly. I guess I don't care what each zone's density is supposed to be, since i used multigrade paper which allows altering those relationships (somewhat). I focus on the high to low range and trying to fit it on the negative, and my final print may not represent the original scene's tonality.

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Originally Posted by Pere Casals

Bill, in fact this is the speed point, I guess, not the film speed.

But it's true that the film speed is calculated directly from the exposure in the speed point. (development also has to deliver the standard contrast to be the ISO speed.)

ISO standarizes the position of the speed point "m" as having 0.1D more density than unexposed areas (fog+base). The film speed instead is calculated from the exposure in the speed point to make an standard meter to aim x10 the exposure in the speed point, this is 3.3 stops.

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By the way where you quote 3.3 you are rounding. It’s 3 and a third.

The 0.1 speed point also needs to meet the contrast parameters. My friend who sold me his sensitometer likes to point out why.

It’s because at the contrast parameters, the speed determined by Delta-X agrees with the speed at the 0.1 point
The speed in both cases now coincides with the outcome of Kodak’s first excellent print studies. That point is the 0.3 average gradient.

I like to point out that 0.1 is certainly easy to find and check. Even though the right place is 0.3 average gradient, it’s harder to mark that on a graph and two people might mark the same curves slightly differently leading to different readings.

So we get a quick reading of the speed by using the 0.1 speed point, and we stay connected with Kodak’s first excellent print studies at the same time.

It was a really good compromise when the 0.1 speed point was chosen... with the contrast parameters.

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Originally Posted by esearing

Not sure that -3.3 stops works for reality.

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From "true speed" definition, a spot at -3.3 will have 0.1D over base + fog, so it will be in the "m" speed point. Pre 1960 ASA change it was -4.3

If that spot has not 0.1D (over base+fog) then it wasn't a "true speed" but an EI (Exposure Index).

...or we had a flawed metering/exposure/processing

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Originally Posted by esearing

If I meter/place textured shadows (dark moss on underside of wet rock, shadowed underside of fallen tree) on zone 2-ish I get no texture. Zones 3-4 give better texture and shadow separation.

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The "Image Quality" we have in the "m" speed point is in the limit yet, grain may be different, etc... one has to know how -4,-3, and -2 looks with his film/process, of course.

But we also have sound inaccuracies in the process:

> A new Shutter had +/-30% specs !

> Is aperture scale exact ?

> Accurate bellows compensation ?

> Did we meter with a probe on the GG ? Have we flare from lens and a from a large circle illuminating compressed bellows ?

> Is film aged ? Is developer aged ? temp/time/agitation control ?

> Are shadows in LIRF because a moderately long exposure ?


If we are very accurate and using a true speed we have -3.3 in the "m". If we are not very accurate then we overexpose (negs) 1 or 1.5 stops and then we are in the safe side. We say "we rate" TMX at 50, but what we do is resurrecting the pre 1960 safety factor !!!! :)

Ho hum... Just more rote stereotypes about films which in fact differ with respect to how deeply down you can dig into the shadows. It can be more than -3.3, and it can certainly be less. And all of this is relative to development protocol. Stronger development (higher overall gamma) typically raises and steepens the toe.

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Originally Posted by Drew Wiley

Ho hum... Just more rote stereotypes about films which in fact differ with respect to how deeply down you can dig into the shadows. It can be more than -3.3, and it can certainly
be less. And all of this is relative to development protocol. Stronger development (higher overall gamma) typically raises and steepens the toe.

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(This is for BW negative film. Slides have a remarkably different norm)


Yes Drew, it can be more or less than 3.3, but if it isn't 3.3 then you are not metering with the true speed of the film/processing.

The calculation of the true speed always uses 10x the exposure in the "m" (B+F+0.1D) speed point to set the meter point. So it's 3.3 or your speed is not the true one.

Another thing is the pool of inaccuracies we have in the metering/processing...

There is sensitometry and there are recipes, both work.

In other words, if you develop exactly normal and meter with true speed then areas at -3.3 will have 0.1D over fog+base. Why? Because ISO norm says it. And a ISO norm is an ISO norm, not tales.

Beware, the BOX speed may be rounded to a standard speed, normative allows it, but then the BOX speed has a little discrepance to the true speed we are speaking, this has also to be said.

I don't give a hoot about "true film speed", as if there is only one valid way to calculate that to begin with. I do care about specific shadow distribution on the toe of the film, which is affected by several variables. And in that respect, I see no substitute to assessing one's own "personal film speed" relative to specific film, developer, and Zone placement (if Zone theory is even used). I've retained four Pentax digital Spotmeters. They all precisely match over their entire range; and if any one of them deviates, I have it serviced. My oldest one is now too beat up to bother keeping alive on life support. But one is kept virtually brand new as a reference. I'm quite confident my meter readings are accurate. My development too. For nitpicky purposes, I'm able to keep dev temp within 1/10th deg F is necessary, which is complete overkill for ordinary work, for which I have a temp compensating timer anyway. Film designers can worry about the rest. And if a batch is off, when I happen to need complete predictability, I'll spot it. But for that kind of usage, best to stick with the majors in terms of quality control - Kodak, Ilford, and Fuji. Then I have lots of densitometer plots confirming the consistency of my own protocols.

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Originally Posted by Drew Wiley

I don't give a hoot about "true film speed", as if there is only one valid way to calculate that to begin with.

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It depends... if you develop like kodak TMX dataheet says you nail the H-D curve they show with real units. I checked it and I found it exact. But if you make a creative development then your true speed can be any.

Also you may want to calibrate what true speed you have with your pocessing... in that case you'll be calculating the true speed to place the "m" at -3.3 again.

If you have an inaccuracy of a full 1 deg F you'll change the contrast, but not much the true speed.

From the analytical standpoint what makes me suspicious of any alleged industry-wide standard is just how different certain companies tend to interpret their "box speed". As much as I like Ilford products, I've found every single one of their films to be rather over-optimistic in terms of rated film speed. They seem to interpolate it too far down onto the toe, perhaps for wish-it-were-so marketing reasons? I dunno. And this seems to be the case in most developers. Then there are those cheaper EU films that are unquestionably marketed using too-good-to-be-true speed ratings. But the kind of technical lab applications I have in mind, Pere, have to be a lot more accurate than anything you're describing. General photography, no.

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Originally Posted by Drew Wiley

certain companies tend to interpret their "box speed".

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Yes of course... Kodak TMax P3200 is 800 true speed, and Ilford Delta 3200 is 1000... to say remarkable examples.

Foma 400 is another example of fake 400 IIRC, and CMS 20 with Adotech II... better at ISO 6.

For this reason it makes sense knowing very clear what's a true speed, because if using it you know where is the "m", and how far an spot in the scene is from m.

Many other films are well rated by the box lettering. We all know what films are...

I call it the BS coefficient. The faster that can be quantified, the better off we all are.

Yes... :)

I could see being suspicious of the speeds in the day of H&D but with ISO speeds I am confident that we can check them.

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Originally Posted by Leigh

Negatives being thin has nothing to do with EI. It's controlled entirely by development.

Shadow detail is a function of exposure and EI, and cannot be changed by development.
- Leigh

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That's what I was told: Exposure changes the shadows and development changes the highlights.

Fomapan 400 was not giving the stated speed on the box, because shadow detail was lacking.
That is a fact that Foma acknowledge in their technical data.
The same could be said for Shanghai. Maybe 50ASA, but not sure if the 4x5 is cut from the same master rolls as the 120 version.
You have to test a film/developer combination before doing any work of importance. So you can be reasonably sure that it will meet your requirements.