Acros in Microphen - and why are ISO ratings inflated? : LUSENET : B&W Photo - Film & Processing : One Thread

Still on my quest for an ISO 100 film that can actually be shot at EI 100 and still get zone I at 0.1 over b+f, the next try is Fuji Acros (only because I happen to have a roll in the fridge!). My trials with Tmax using HC-110, Rodinal and Microphen resulted in speeds between about 32 and 80!

Anyone tried Acros in Microphen and if so, what EI, developer, time and temperature did you use? It's not listed in the good old "massive development chart" and a web search didn't turn anything up either. I doubt it will reach 100 speed even in microphen, but since I have it on hand, it's worth a test.

The second part of my question is why ISO ratings are so inflated? I thought that the ISO standard was based on 0.1 above b+f when the film is developed to some standard CI value. I doubt I could get true 100 speed out of most ISO 100 films if I left them in Microphen all day and developed to a CI of 1.0. My consistant experience has been that any film I test is actually rated about 1/2 what's on the box with any sort of "normal" development. How do the film companies manage to come up with such inflated ISO numbers, or is the ISO number not based on 0.1 above b+f to determin the speed point?

-- Bob Atkins (, February 12, 2002


"The second part of my question is why ISO ratings are so inflated?"

Maybe it's your technique/equipment? This is why testing is so important. I shoot 120 size TMX at EI 100 and develop in Xtol 1+2 and get plenty of shadow detail. I haven't used a densitometer but I like what I see.

-- Tim Brown (, February 12, 2002.

True, but ISO rating is supposed to be a standard. It's not based on "getting plenty of shadow detail". That's a subjective opinion. ISO standards are supposed to be objective. Pretty much every book and article I've read on film testing, from Ansel Adams to [insert your favorite film tester] has reached the conclusion that if you 1/2 the marked ISO rating you'll be about right when it comes to exposure.

-- Bob Atkins (, February 12, 2002.

> about 32 and 80!

Yep, that's about right; for most developers I've tried with it I get EI 64.

As for the ISO rating, it used to be that a specific developer and development process was spelled out to be used for ISO rating but the problem was that it was pretty useless for pictorial use because using that process gave very high contrast (and commensurate higher "speed").

That's been changed and manufacturers can use whatever they long as somewhere or other thay specify what and how. Plus it's not a given they're using the classic .10DU.

Why is it done this way? Marketing. You bought "Acros 100" while you wouldn't consider "Acros 50," right?

-- John Hicks (, February 12, 2002.

But I though ISO standards were, in fact, standards, set by the International Standards Organisation. If every film maker can measure speed by their own method, how can they call it ISO? Companies can't define their own ISO 4000 quality standard!

Even if the "standard" was set for high contrast (which is what I remember too), that's really not going to double a film speed. They're just overdeveloping it, which ups contrast but doesn't usually do a lot to the 0.1 over b+f speed point.

There is an ISO document ISO 6:1993 "Photography -- Black-and-white pictorial still camera negative film/process systems -- Determination of ISO speed" which I presume contain the ISO film speed definition, but the contents of the document don't seem to be available on the web (unless you pay ISO 44 swiss francs to see them!).

-- Bob Atkins (, February 12, 2002.


You are right. The standard is set by the International Standards Organization. It's not based on the 0.1 over b+f standard, that's your EI which is a completely different thing.

Some certain manufacturers that put their film in a yellow box hold fast to the ISO standard and are apparently ignorant of the fact that for most photographers it's only a starting point.

On the other hand, notice that Ilford and Bergger and others don't refer to ISO numbers. They call them EIs when they use any term at all. For example, Ilford doesn't make any claim that FP4+ is a 125 film period. They recommend 125 as a starting point and offer development times for 50 and 200 as well.

-- David Parmet (, February 12, 2002.

Well, I got this from the archives:

Quoting Frances Shultz in November 1998 issue of Shutterbug:

"...ISO film speeds are determined according to the amount of light which is required to give a fixed density (0.10 above film base plus fog) at a fixed contrast (effectively a G-bar or C.I. of 0.615).."

So he thought the ISO speed point WAS 0.1 over b+f. I guess the only way to know for sure is to get hold of a copy of the ISO standard.

-- Bob Atkins (, February 12, 2002.

Avoid entering any situation where your good health depends on the accuracy of your iris control, your shutter speed control, or the accuracy of the ISO rating on the box. I'd be willing to bet that each of those quantities has manufacturing tolerances. Does any one of you know what is the actual value of any of these qualities when you set it? How much precision are you expecting? How much do you think you really need? Who told you so? How would you find out the accuracy of your camera settings without using film?

-- Patrick A. Gainer (, February 12, 2002.

Well he's wrong but only in the strictest semantical sense of the word.

If I were a Zone System purist, which I am sometimes but not all of the time, I would be remiss not to remind you that there are a lot of terms bandied about in photography that have no real quantitative meaning or relevence - words like ISO film speed.

The actual ISO standard has very little to do with photoraphy and more to do with sensitometry - the study of the affects of light energy on photo-sensitive materials. A good introduction if you are so inclined is Todd and Zakia's "Photographic Sensitometry". It explains where the standard comes from. I could reprint it here but it goes on for pages and we'd all have to hold our heads together so they don't blow up.

Exposure Index is a more practical - Zone System - term which is your own personal speed for a particular film / developer combination based on your practices, the water quality in your darkroom, the way you agitate, and a bazillion other variables.

But in practical terms, when you arrive at a film speed that works fine for you regardless of how you got there (trail and error or densitometer) it's your EI and you should stick with it as long as it works.

And don't worry about the terminology or whether or not Kodak is lying to us.

-- David Parmet (, February 12, 2002.

Tollerences are fine, but if all the rating are off by a factor of 2, it's not tollerences that are "at fault".

It's true enough a film speed is whatever YOU determin it to be for YOUR application, but that doesn't help a lot when your application is for 100 speed film and every 100 speed film (as "marked on the box") actually rates somewhere around 50.

Now if there were a 200 speed B&W film, I'd just go out and buy that, comfortable in the knowledge that it was inflated by a factor of 2 and that I could shoot it at 100 and get what I wanted. However my choices seem to be 100 film shot at 50 or 400 speed film shot at 200!

What's the point of an ISO standard if nobody actually agrees that the numbers it generates are particularly useful? I suppose it's slightly better than film that comes in a box marked "Speed? We don't know, figure it out for yourself", but not by much. Even the suggested developing times given by most manufacturers are off. How many people here shoot at the "official ISO" and develop the "official" time and temperature as stated by the manufacturer?

-- Bob Atkins (, February 12, 2002.


Don't confuse ISO with anything to do with the real world. ISO standards apply to various manufacturing and technical processes. There's an ISO standard for just about everything from what constitutes a 60 watt light bulb to how the wires in Cat 5 cables are twisted. They are there to ensure consistancy and nothing else.

So to your point.... with ISO standards I know for certain that a film with an ISO speed of 100 requires more exposure than a film with an ISO speed of 400. Nothing more or less. To actually find how I should expose the ISO 100 film to get a negative with sufficiant shadows and printable highlights is an entirely different matter. That's based on my own personal practices and equipment.

And to your point about a true 100 speed film - 64 to 100 is only 2/3 of a stop. In the grand scheme of things that's not much of a difference anyway. You can shoot Plus X -- rated at 125 by Kodak but with a true EI between 80 and 100.

-- David Parmet (, February 12, 2002.

To be technically correct...

There is no such thing as "ISO 100." There is "ASA 100," "DIN 21," and "ISO 100/21." There should be a degree sign after 21 in these examples.

The details of measurement methods have changed. Notation has changed.

Also, I have seen several ISO 100/21 film that appear to be actually faster than the designated speed. (All color negative though)

-- Ryuji Suzuki (, February 12, 2002.

Bob, I don't keep current on the speed stuff, but I can quote from ANSI PH2.5-1972 {"…Method for Determining Speed of Photographic Negative Materials (Monochrome, Continuous-Tone)"; dated 1972} if that helps any. Some of the key points are reaffirmed in the 1997 IS&T Handbook of Photographic Science and Engineering, which is probably about as close to a bible as the photographic industry has. They say the same speed formula "… is also adopted in International Standard ISO 6…". I doubt that anything significant has changed since then. In fairly recent history, the changes (ANSI) seem to have been things like moderate changes in the pH and buffering capacity of the developer, etc.

John Hicks says, "That's been changed [specific developer, etc?] and manufacturers can use whatever they want... …". He may know something about this that I don't, but I think it's more likely he's heard something about COLOR negative standards and mistakenly presumed they were a change to the "monochrome, continuous-tone" negative standard. (Please correct me if I'm wrong, John.)

Basically, Frances Shultz' quote (in your excerpt) seems to be pretty much correct. That is, the film is developed such that when 1) you find a point on the "characteristic curve" that has a density of 0.10 above "base plus fog" and 2) you move 1.30 units over on the log(10) exposure axis the film density has increased by 0.80. On such a sample, the 0.10 density above base + fog IS the speed measuring point. This represents, to me, pretty "normal" contrast; a slope of about 0.80/1.30 = 0.615 if it were a straight line. Note that the 1972 ANSI standard specifies the delta 0.80 +/- 0.05.

FWIW, Richard Henry, in his book "Controls in Black and White Photography" has a fair amount of history on ANSI/ISO speed (monochrome neg film) standards. He indicates that some of the developer changes (pH, buffering, etc) had to do with the specified formula producing erroneous speeds on certain films. I don't have any good ideas on what you are seeing but this could be related. There may be errors in manufacturer's ANSI/ISO ratings on film, but I doubt it.

FWIW, the 1972 ANSI standard (and I presume all the more recent ones as well) addresses many of the variables in the system. As an example, the test sample must have reached equilibrium at 20 deg C and relative humidity of 60% +/- 10%. The light source is specified, exposure time must be between 1/20 and 1/80 second, holding period between exposure and development is specified, etc, etc. The developers of the standards are more savvy than many people give them credit for.

-- Bill C (, February 12, 2002.


"Some certain manufacturers that put their film in a yellow box hold fast to the ISO standard and are apparently ignorant of the fact that for most photographers it's only a starting point."

I don't know which Kodak film(s) you're referring to. The box of TMX I just checked says EI 100; there's no mention of ISO. Also, as I posted in another of Bob's threads asking about the true speed of TMX, I achieve an actual 100 in Ilfosol-S (based on the classic 0.1 criterion), rotary, 1:14.

-- Sal Santamaura (, February 12, 2002.


I'm holding a box of Tri-X that says ISO 400/27(o) and a box of Verichrome Pan that says ISO 125/22(o).

Ilford also states ISO film speeds (can you believe that in my third hand I'm holding a box of FP4+ that says ISO 125/22(o)?) but for processing times offers a range of EIs from 50 to 200. Kodak seems to assume you are either shooting at 400 for TriX or 125 for VP or you can figure out an appropriate EI for yourself.

I've never used the Tmax films so I can't state for certain what's on those boxes.

-- David Parmet (, February 12, 2002.

> He may know something about this that I don't

No, I don't; I was paraphrasing something I'd read somewhere or other from someone who had read the appropriate ISO docs past and present. I have no idea who, what, where or when. That's my story and I'm 'a stickin to it.

I too was rather disappointed to find that Acros 100 was more like Acros 64 or Acros 50....not that it would be a bad EI 64 or 50 film, but...

-- John Hicks (, February 13, 2002.

Phil Davis' "Beyond the Zone System" also confirms that the ISO/ANSI standard uses 0.1 over b+f (when developed to a CI around 0.6) as the speed point.

I checked my TMZ box and indeed, it is an EI 100 film, not an ISO 100 film! On the film cassete (35mm) it just says 100/21 and doesn't mention EI or ISO. On the other hand, Tri-X is ISO 400 and FP4+ and HP5+ are also ISO, as is Acros.

I'm just glad I don't need to shoot my Sensia 100 at EI 50 too! At least slide films are pretty much "as advertised". Of course they use a different standard for film speed too.

-- Bob Atkins (, February 13, 2002.

> ISO/ANSI standard uses 0.1 over b+f (when developed to a CI around 0.6) as the speed point.

See what's different? We usually don't develop to such a high CI and when we develop to a lower CI the .10DU speed drops a little.

This parallels the usual gripe about Agfa Rodinal; when film's developed according to Agfa's recommendations the negs are bulletproof and the reason is that Agfa's recommendations result in a CI of .65. So when the negs are developed to a CI of .50 in Rodinal the EI's quite a bit lower.

-- John Hicks (, February 13, 2002.

Well my last attempt at TMX in Microphen resulted in a CI close to 0.7 (my dev time was too long) and I STILL didn't get 0.1 over b+f for zone 1 at EI 100!

-- Bob Atkins (, February 13, 2002.

What's the light source (wavelength used for measurement)?

Also, how's your unit and calibration of the density measurement??

-- Ryuji Suzuki (, February 13, 2002.

> However my choices seem to be 100 film shot at 50 or 400 speed film shot at 200!

Are you referring to developing EI 400 film in such a way that a side-effect is EI 200 or do you generally have to use EI 200 for EI 400 films with no special development?

-- John Hicks (, February 13, 2002.

(1) I rate both HP5+ and Tri-X at EI 200 developed in my standard soup (HC-110 diluted 1:43). That's what gives me 0.1 above b+f at zone 1. With Microphen I can push the EI to around 400.

(2)My densitometry readings are based on two sources. First a Minolta Autometer IIIF. You can measure changes in transmission to 1/10 stop, then the change in OD is log(2^(change in stops)). Second I use a Perkin-Elmer Lambda 9000 UV/VIS/NIR spectrophotometer calibrated to NIST standards and I average density over the 450-600nm range. Note that I use the Minolta at home and the Perkin-Elmer at work! The two methods give suprisingly close results.

-- Bob Atkins (, February 14, 2002.

"It's true enough a film speed is whatever YOU determin it to be for YOUR application, but that doesn't help a lot when your application is for 100 speed film and every 100 speed film (as "marked on the box") actually rates somewhere around 50. "

You should be happy. You know something that no one else knows. You know that you should set your exposure meter at 50 for VERY box of film that says 100.

-- Patrick A. Gainer (, February 14, 2002.

The problem is that just about everyone (including Ilford and Kodak) knows it!

I once found an interesting article on the web about how to do a zone system calibration test for film and prints, written by a well known and well respected author (of course I can't remember his name right now!). He said that if you DIDN'T get about 1/2 the claimed film speed, you should check your test results. If you couldn't do a film test for some reason, rating it at 1/2 the published speed should put you right in the ball park. He was right.

The point of a standard is just that. It should be a standard. If every meter rule you bought was 50cm long, you'd have grounds for complaint, even though you (and everybody else) knew the conversion factor was 2x.

Not that it matters, I'd just like a 100 speed film that didn't need you to try 15 different developers to get 100 speed. In the end it doesn't really matter what's written on the box I guess. Just give me something I can slosh around in a tub of HC-110 that's finer grain than HP5+ and has a true speed no slower than 100 and I'll be happy!

-- Bob Atkins (, February 14, 2002.

Bob, why you want to stick with HC-110?

-- Ryuji Suzuki (, February 14, 2002.

> 1) I rate both HP5+ and Tri-X at EI 200 developed in my standard soup (HC-110 diluted 1:43). That's what gives me 0.1 above b+f at zone 1. With Microphen I can push the EI to around 400.

OK, next question: how have you calibrated your light meters and how are you exposing your test strips? Or iow, why does our mileage vary?

I've calibrated all my reflected-light meters to sunny f16 reading a Wallace Expo-Disc and all incident-light meters to sunny f16 in incident mode.

Taking HP5+ as an example, (I don't use HC-110) I get usually EI 400 or 320 in "normal" developers with the film developed to the usual "N" specs and the only major deviations for N development have been EI 160 for D-23 1:3 and EI 640 for both Microphen and DD-X.

-- John Hicks (, February 14, 2002.

Well my meter gives a "sunny f16" reading on the clear blue northern sky and I get excellent exposure on Sensia 100 slide film rated at EI 100, so I'm pretty sure they can't be more than about 1/3 stop off, if that much.

I expose my "zones" by imaging a uniformly illuminated wall at +3 stops to -4 stops from the meter reading to give me zones I through VIII.

Why HC-110? Well, it was good enough for Ansel Adams, so it's good enough for me. More seriously it lasts almost forever as concentrate, is quite versatile wrt dilution and I quite like the look it gives with Tri-X and HP5+. I also have Rodinal and Microphen on hand. I tried XTOL and, like many others, had problems with it. You have to draw the line somewhere when it comes to stocking different developers.

BTW though HC-110 "lasts forever" my recent tests were all done with a fresh bottle.

-- Bob Atkins (, February 15, 2002.

I think the real problem is not just the developer because you are getting lower speed than what Microphen should get.

However, HC-110 is the developer that even Kodak implicitly (or explicitly but in indirect words) admitted that it can't deliver full speed with TMY though they claim to deliver rated EI400 with D-76 and other standard developers.

I'm confused who was using 35mm only, but I didn't like HC-110 for 35mm after using it for a while. It looked pretty nice with FP4+ but then I don't use FP4+ any more. I still have some five-year old HC-110 left in my shelf but I don't use it except for APX25 in 120, which isn't a bad combination. Don't you think you'd be happier if you find something that works even if you are never going to finish your bottle of HC-110??

-- Ryuji Suzuki (, February 15, 2002.

FWIW You know, when I was a lot younger, like 40 years ago, the ASA numbers were bumped up. I think TX went from 200 to 400, PX went from something up to 125, I think. And all the photographers went into an ecstacy because ASA was now closer to "true".

I never could see that, but then there are a lot of things I have not seen through the years

-- Richard C. Trochlil (, February 16, 2002.

Moderation questions? read the FAQ