A Lazy Man's Zone System

0x001688936CA08 said:

Why do you want to find a "personal ISO" anyway?

Click to expand...

Indeed. Companies like Kodak and Ilford have already done the work, follow what's in the data sheet and it will give good negatives.

Craig said:

Indeed. Companies like Kodak and Ilford have already done the work, follow what's in the data sheet and it will give good negatives.

Click to expand...

I thought the real-world ISO of the film depends on how you develop it. The data sheets for the Foma films even have a bunch of plots with "ISO" on the y-axis and "development time" on the x-axis for four different developers. It sure makes it sound like ISO is a film's ISO is a completely individual thing --- something tied to what developer you use and how you develop.

EDIT: Example: https://www.digitaltruth.com/products/foma_tech/Fomapan_400.pdf

There is a method of determining speed that is defined in the ISO standard, and yes that is developer dependent. The developer used is given in the testing, and the various data sheets will specify a developing time and speed obtained, as well as contrast index.

However, there is a concept of EI: Exposure Index. That can be an effective speed based on how you agitate, developer etc, etc. However, that isn't based on the ISO standard speed.

Foma 400 isn't a great example, as it is known to not give 400 speed when tested under ISO conditions, it's more in the 200-250 range.

What Craig said.
A big part of the problem is that people use the term "ISO" where they ought to use Exposure Index ("EI") when they speak about their personal choice of film sensitivity when they set their meter.
No one really has a "personal ISO" for a film and developer combination. Many people have a "personal EI" for a film and developer combination. The ISO specification sets out how to actually determine an actual, non-personal ISO for a film and developer combination.
FWIW, while the actual ISO for a film and developer combination does vary with developers, it takes a fairly radical change in type of developer to make a big difference.
Historically, D-76 was specified for ASA/ISO determination of speed, but with the advances with more modern film and developer technology that became less useful. As a result, the ISO standard was changed in order to permit use of particular developer with particular films.
I've posted about this, off and on for years.
King Canute comes to mind...

These curves do not represent independent results. While someone provide technical definitions, I’d like to put it simply: early in development, highlight density rises faster than Dmin; later, Dmin increases more rapidly. When highlight density growth slows while Dmin continues to rise, that’s roughly the film’s “optimal” ISO. For Fomapan 400 with common developers like D-76 or XTOL, the curves indicate an optimal ISO (or more accurately, EI)) of about 200–250, which aligns with the manufacturer’s recommended times. The box speed of 400 is overstated—unlike most Kodak or Ilford films. If you run a zone test with D-76, you’ll likely find that just 200–250 EI yields best detail.

From this “optimal” point, you can push (extend development, raising Dmin), pull (shorten development, lowering highlight density), or use speed-altering developers (though these are less 'standard' due to grain, storage, cost, or handling issues). These EI adjustments are all workable, but each involves trade-offs. The impact depends on your needs and whether you see these changes as creative opportunities.

dcy said:

I thought the real-world ISO of the film depends on how you develop it. The data sheets for the Foma films even have a bunch of plots with "ISO" on the y-axis and "development time" on the x-axis for four different developers. It sure makes it sound like ISO is a film's ISO is a completely individual thing --- something tied to what developer you use and how you develop.

EDIT: Example: https://www.digitaltruth.com/products/foma_tech/Fomapan_400.pdf

Click to expand...

Foma is indeed problematic. They should have used EI (exposure index) rather than ISO. On each of their graphs there will be one exposure index that meets the ISO criteria and that will roughly be the one with a gradient of 0.62.

In general a film will have one ISO speed +/- relatively minor deviations depending on what developer is chosen (assuming general purpose developers and barring “extreme” processing procedures).

The ISO standard used to specify a specific developer formula. That requirement was removed in the 1993 revision. The manufacturer is free to chose the developer but must disclose the information upon request.

For a few mostly historical reasons (mainly the Zone System not having been updated when the former safety factor was removed from B&W film speed standard in 1960), the Zone System EI (or so called “personal EI”) is 2/3 stop lower than the ISO speed by definition. The typical “personal EI” Zone System test therefore isn’t really revealing anything. It’s no coincidence most people who do these tests carefully/properly end up with personal EIs in the range of 1/2 to 1 stop lower than the ISO speed. That’s just how it should work out. It’s not a bad approach particularly with larger film sizes because it gives you a safety margin against underexposure.

The John Finch EZ method (based on the minimum time to max black procedure) will lead to more variable EI results as the criteria are different.

An EI can be anything you want based on whatever criteria. The ISO speed has specific criteria. It should be noted these criteria are not arbitrary. They have their lineage in print quality. Whether or not one chooses to set the meter to the ISO speed, the ISO speed IS grounded in the real world. People sometimes mischaracterize it as some sort of laboratory thing (or worse, a conspiracy) that doesn’t apply to the real world and this leads to the assumption us perfectionists with higher standards need to find a real EI at the outset. Few people really understand the tests they run or what the results mean.

Of course we all have our preferences when it comes to enlarging or scanning negatives, which makes perfect sense, and that is how one should find their personal EI - over time assuming the metering is going ok, if one finds his/her negatives consistently too thin or needlessly dense, adjust the EI.

Some kind of average metering along with multigrade paper worked for me:

Craig said:

However, there is a concept of EI: Exposure Index. That can be an effective speed based on how you agitate, developer etc, etc. However, that isn't based on the ISO standard speed.

Foma 400 isn't a great example, as it is known to not give 400 speed when tested under ISO conditions, it's more in the 200-250 range.

Click to expand...

Alternatively, Foma 400 is a great example of the unreliability of "box speed"

I chose Fomapan 400 specifically because its real world speed is wildly different from what it says on the box. It's crazy that Foma's own plots that they publish on their own datasheet show that Fomapan 400 is closer to ISO 250.

MattKing said:

What Craig said.
A big part of the problem is that people use the term "ISO" where they ought to use Exposure Index ("EI") when they speak about their personal choice of film sensitivity when they set their meter.
No one really has a "personal ISO" for a film and developer combination. Many people have a "personal EI" for a film and developer combination. The ISO specification sets out how to actually determine an actual, non-personal ISO for a film and developer combination.
FWIW, while the actual ISO for a film and developer combination does vary with developers, it takes a fairly radical change in type of developer to make a big difference.
Historically, D-76 was specified for ASA/ISO determination of speed, but with the advances with more modern film and developer technology that became less useful. As a result, the ISO standard was changed in order to permit use of particular developer with particular films.
I've posted about this, off and on for years.
King Canute comes to mind...

Click to expand...

Let me try to summarize and please tell me if I got it right:

• ISO is 95% a inherent property of the film, with only small contribution from the developer.
• EI is what you set I set my camera light meter to in order to get photos I like.

Is that more or less the difference?

Milpool said:

Of course we all have our preferences when it comes to enlarging or scanning negatives, which makes perfect sense, and that is how one should find their personal EI - over time assuming the metering is going ok, if one finds his/her negatives consistently too thin or needlessly dense, adjust the EI.

Click to expand...

Aha! Thanks.

That's a strategy I can follow and makes sense to me: If my negatives are consistently too thin or too dense, adjust the EI.

dcy said:

Let me try to summarize and please tell me if I got it right:

• ISO is 95% a inherent property of the film, with only small contribution from the developer.
• EI is what you set I set my camera light meter to in order to get photos I like.

Is that more or less the difference?

Click to expand...

Basically, although you should be careful about picking a particular percentage!

dcy said:

Aha! Thanks.

That's a strategy I can follow and makes sense to me: If my negatives are consistently too thin or too dense, adjust the EI.

Click to expand...

This too.

The rest of this post should probably be mostly put aside by you until you have a little bit more experience, and have arrived at more of a sense of what works for you.

One caveat to both points: with many films and developers, you can tailor the response a bit by using different EIs, and adjusting the development.
Each adjustment means compromises, but with experience, and after arriving at personal preferences with respect to how you like your results, you can make choices and get some variety in your results.

As an example of how the compromises and variability shakes out, consider the EI 3200 films - Kodak T-Max 3200 and Delta 3200 - which are specifically designed for that. Each of them actually has an ISO rating of 800 or 1000, but they are not really designed/optimized to be used at those ISOs - they don't IMHO give attractive results if you meter at those settings. Instead, they are optimized for use at EIs between 1600 and 3200, with associated increased ("push") development. The shadow detail loss that comes from that under-exposure when used at those EIs doesn't go away (mostly) but their mid-tone and highlight rendition actually improves.

With "normal" films like HP5 or T-Max 400. if you use an EI of 1600, you will lose similar amounts of shadow detail, but a 2 stop push development will, IMHO, cause the mid-tone and highlight rendition to degrade much more than with the EI 3200 films.
In other words, the compromises change.

With respect to the aforementioned personal preferences, some come from "personal vision" and some come from printing/darkroom preferences.
When my Darkroom Group get together, we often show prints and discuss negatives. If each of us each lay out a sheet of our negatives on the big light table where we meet, we can often tell which negatives belong to which photographer, because we are well aware of each other's preferences. Mine tend to be the result of a bit less exposure, and a bit less development than most. A long time friend, who used to make high volumes of prints for his work, prefers much beefier negatives. Both of us admire the other's prints.

All of which are refinements. My strong advice would be to work first toward a "normal" that you are happy with, which is around the "normal" that the manufacturer's recommendations are targeted towards. The big manufacturers like Kodak, Fuji and Harman/Ilford base those recommendations on print viewing criteria experiments that formed the basis for the ASA/ISO standards.

dcy said:

Alternatively, Foma 400 is a great example of the unreliability of "box speed"

Click to expand...

It's a case of a manufacturer playing fast and loose with terminology.

Kodak, Ilford and Fuji base their speeds on the ISO standards, and say when they don't. Ilford for some of their films say that the speed is based on practical evaluation, not the ISO standard. As a general rule, any film from those 3 makers has a reliable box speed.

Foma's box speeds are seriously unrealistic.

dcy said:

Let me try to summarize and please tell me if I got it right:

• ISO is 95% a inherent property of the film, with only small contribution from the developer.
• EI is what you set I set my camera light meter to in order to get photos I like.

Is that more or less the difference?

Click to expand...

Yes. Film is designed to have a certain ISO. The parameters are specific. Manufacturers can give a film an ISO when they hit the development conditions. Here’s a transcription of the FP4+ curve from Ilford’s specification sheet. They had to hit the tip of that triangle with the curve plus or minus 0.050

I think they aimed to the high side of tolerance to get the highest possible speed within conditions

dcy said:

Alternatively, Foma 400 is a great example of the unreliability of "box speed"

I chose Fomapan 400 specifically because its real world speed is wildly different from what it says on the box. It's crazy that Foma's own plots that they publish on their own datasheet show that Fomapan 400 is closer to ISO 250.

Click to expand...

The thing you have to remember is that the test plots are done under an effectively flare free environment that does not account for internal emulsion halation/ turbidity. Those effects in real-world usage could add 2/3 stop or so of internal flare which you would need to compensate for via exposure & process. If you try to expose a film that has those characteristics at the 'correct' test chart speed you may find all sorts of problems with highlights and contrast that will not be resolved by adding more exposure (which is always the first port of call under Zone System ideology, unfortunately). It's not that Foma's data is in contradiction to the speed printed on the box, but they are attempting to account for end user behaviour relative to a (budget) product. The Zone System is often more reliant on manufacturers' anti-halation measures than people realise (and if I was more cynical, I might suggest that many of Adams' film choices related more to their anti-halation characteristics rather than curve behaviour).

dcy said:

I chose Fomapan 400 specifically because its real world speed is wildly different from what it says on the box. It's crazy that Foma's own plots that they publish on their own datasheet show that Fomapan 400 is closer to ISO 250.

Click to expand...

It’s an example where the data sheet used weasel words to describe its speed. Nominal 400 is not the same as the trustworthy 400 you get with TMAX 400

The datasheet doesn’t even indicate that it ever reaches 400. So I am left to wonder why the film has been given a box speed of 400

Bill Burk said:

So I am left to wonder why the film has been given a box speed of 400

Click to expand...

Internal flare effects boosting usable (not actual flare-free) shadow speed. You'd need to load it down with more effective absorber/ anti-halation dyes etc to get it to perform well at 160-200.

All the budget BW films reduce their internal anti-halation (probably because those are some of the most expensive components). It is more noticeable in the thicker/ faster emulsions. You can see similar behaviour in the Kentmere range.

Lachlan Young said:

. It's not that Foma's data is in contradiction to the speed printed on the box, but they are attempting to account for end user behaviour relative to a (budget) product.

Click to expand...

Is this not something that other makers such as Ilford and Kodak need to take account of then? Or are there other reasons why it doesn't apply to Ilford and Kodak so that in terms of end-user behaviour all are being honest?

Thanks

pentaxuser

Lachlan Young said:

Internal flare effects boosting usable (not actual flare-free) shadow speed. You'd need to load it down with more effective absorber/ anti-halation dyes etc to get it to perform well at 160-200.

All the budget BW films reduce their internal anti-halation (probably because those are some of the most expensive components). It is more noticeable in the thicker/ faster emulsions. You can see similar behaviour in the Kentmere range.

Click to expand...

Hi Lachlan, I don't think that flies (as they say). Leaving aside the fact this is not in the ISO standard (meaning Foma should be using "EI", not "ISO", from a practical perspective it doesn't make sense. Halation is not the same as a flare factor. While flare does increase effective threshold speed, halation does not as it is within the emulsion and therefore localized.

Milpool said:

Hi Lachlan, I don't think that flies (as they say). Leaving aside the fact this is not in the ISO standard (meaning Foma should be using "EI", not "ISO", from a practical perspective it doesn't make sense. Halation is not the same as a flare factor. While flare does increase effective threshold speed, halation does not as it is within the emulsion and therefore localized.

Click to expand...

Internal flare/ reflections are consistent with making an emulsion thicker/ faster - and adding an extra layer of emulsion can cause further reflections at the boundary between them - I was being imprecise by adding a reference to anti-halation rather than purely referring to absorber dyes. The point (I think) remains - it seems clear that if you don't use absorber dyes, and specified EI is stuck to, a higher effective speed (by riding the internal reflection effects) is feasible at various grain/ sharpness/ latitude costs of varying severity. The effects of exposure overload along object boundary edges on Fomapan are visually quite distinctive and 'leak' in the manner we would normally characterise as halation.

Craig said:

Ilford for some of their films say that the speed is based on practical evaluation, not the ISO standard.

Click to expand...

Ilford's sloppy phrasing makes it easy to conclude that, but they are actually referring to their stated EI values coming from acceptable camera settings in real world situations and not actual film speeds under those conditions. "It should be noted that the exposure index (EI) range recommended for HP5 Plus is based on a practical evaluation of film speed and is not based on foot speed, as is the ISO standard."

Stephen Benskin said:

"It should be noted that the exposure index (EI) range recommended for HP5 Plus is based on a practical evaluation of film speed and is not based on foot speed, as is the ISO standard."

Click to expand...

What Ilford films base their speed on foot speed and what speeds are based on practical evaluation and is there a standard and recognised way to do this? I had thought that only D3200 was not based on the ISO standard

So in the case of HP5+ is the box speed of 400 based on foot speed? I was unsure what you meant by the EI range recommended. Is that range of speeds that Ilford states development times for in its film specs. If so I understand that and would be surprised if anyone thinks there can be more than one ISO speed for any film anyway

Thanks

pentaxuser

pentaxuser said:

What Ilford films base their speed on foot speed and what speeds are based on practical evaluation and is there a standard and recognised way to do this? I had thought that only D3200 was not based on the ISO standard

So in the case of HP5+ is the box speed of 400 based on foot speed? I was unsure what you meant by the EI range recommended. Is that range of speeds that Ilford states development times for in its film specs. If so I understand that and would be surprised if anyone thinks there can be more than one ISO speed for any film anyway

Thanks

pentaxuser

Click to expand...

I don't think it helps for Ilford to call it foot speed, but yes. The data sheet clearly shows HP5 Plus as ISO 400.

EI refers to the camera setting. Here's the entire paragraph from the data sheet.

EXPOSURE RATING
Best results are obtained at EI 400/27, but good image quality will also be obtained at meter settings from EI 400/27 to EI 3200/36. It should be noted that the exposure index (EI) range recommended for HP5 Plus is based on a practical evaluation of film speed and is not based on foot speed, as is the ISO standard.

It's saying basically the same thing as with D3200. It has been determined (non-sensitometrically) that acceptable / good results are obtainable if the camera is set to EI X, not that the film speed is EI X. The speed of the film is the ISO and how the camera can be set is the EI. Ilford is using the terms correctly. They could just communicate it better. There always seems to be a compromise between being scientifically accurate and being understood by the general public.

The HP5 document also refers to the ISO speed:

Although rated at ISO 400/27º, HP5 Plus can produce high quality prints when exposed at meter settings up to EI 3200/36 and given extended development in ILFORD ILFOTEC DD-X, ILFOTEC HC, MICROPHEN or RT RAPID developers.

For some of the films the wording is clearer so I think it’s just a matter of inconsistent writing. FP4 for example:

FP4 Plus has a speed rating of ISO 125/22º to daylight. The ISO speed rating was measured using ILFORD ID-11 developer at 20ºC/68ºF with intermittent agitation in a spiral tank. Best results are obtained at EI 125/22, but good image quality will also be obtained at meter settings from EI 50/18 to EI 200/24. It should be noted that the exposure index (EI) range recommended for FP4 Plus is based on a practical evaluation of film speed and is not based on foot speed, as is the ISO standard.

Note: My transcription of the Ilford data sheet curve depends on the published curve being accurate. I divided the exposure axis into ten divisions and then calipered to the middle of the thick curve line at each crossing.

Then I set the speed scale to where the foot crosses 0.1

I didn’t actually process and graph my own results. I am curious to see how that will compare.

Last time I bought a couple boxes of paper the seller included a roll of HP5+, so I will test it sometime soon.