"Real" ISO values of sheet film.

[Sirius Glass]

As PE said [and others] the ISO is the real speed. If you need to use your personal EI, it is for one or more of the following reasons:

1. Your lightmeter needs to be calibrated.
2. Your camera needs shutter work done. Get you shutter calibrated.
3. You have lousy lab technique.
4. You has an Operator Assisted Failure [Read: OAF].
5. You are a Zonie and you have nothing better to do with your life then endlessly test film.

This is not a complete list, you those of you who are smart enough will figure out the patterns.

cheers,
Steve

 

[Chuck_P]

You are a Zonie and you have nothing better to do with your life then endlessly test film.

In the words of Col. Potter----horsehockey! Spoken by a devout Zonie.

 

[MattKing]

It seems to me that the ISO is a real speed - not the only one.

What ISO gives you is a very useful comparable - determined under well defined laboratory conditions that are not identical to the conditions in your workflow, but reasonably similar to conditions found in real life.

It is not at all surprising that your carefully determined EI for a film would differ from the ISO for that film - because your tests are not performed in the same conditions as the ISO tests are performed in. But that doesn't mean the ISO speed isn't real.

 

[Photo Engineer]

Well, guys, it is not hard to understand why we got to "experiment" at home with as much free film as we wanted. I would routinely test a film for speed in the lab at work, and then take a sample home to shoot in my trusty Nikormat EL and then compare the results regarding ISO. I would process a lot of it here at home too, just to compare workflow.

What I can say is that developed to the same contrast using the same developer, I was able to duplicate at home what I got in the lab. This ranged across films and papers from D-76, Dektol and Harder Fix for B&W and across E4, C-22, C-41 and E6 for color along with Etaprint C and Ektaprint 3. I used the recommend time/temperature charts published in the dataguides. This included later on, besides 35mm, some sheet film (4x5 Ektacolor S) and 120. I've used SS reels, Jobo and other methods, and fiddled around in-between. As long as the basic contrast was obtained as shown in the dataguide, I had the same speed.

This includes coatings that I made myself, as well as the stock items from our supply. It included FE (Full Width experiments) and FW (Narrow experiments) - I know, the abbreviations are not right but that is the way the plant said to call them! I've also coated and tested from many of the KRL coating machines and truly ISO = ISO, the ANSI standards and all the other things. We had an aim curve, an aim exposure including time, color temperature and a whole host of other parameters and we matched this or else!

PE

 

[Hikari]

Box speed is the true speed. If you find that is not the case for you, look at your system--it isn't the film. I am always amazing that people disparage the same science that brings you the technology you use. If you think there is is a difference between the science and the "real world," you have probably misunderstood the science.

 

[Stephen Benskin]

It seems to me that the ISO is a real speed - not the only one.

What ISO gives you is a very useful comparable - determined under well defined laboratory conditions that are not identical to the conditions in your workflow, but reasonably similar to conditions found in real life.

It is not at all surprising that your carefully determined EI for a film would differ from the ISO for that film - because your tests are not performed in the same conditions as the ISO tests are performed in. But that doesn't mean the ISO speed isn't real.

jnanian, you might want to re-read Ron's post. It doesn't support your position. The photographic myth is that just because it is scientifically tested, it somehow doesn't correspond to real world conditions. Funny how no one ever seems to think that about color reversal film speed.

Matt, exactly, an individual's use of the film can have an affect on the effective film speed, but film speeds were determined using psychophysical testing. They started with finished prints and worked backwards; therefore, they reflect the conditions of the real world.

What concerns me about these kind of discussions is there is very little critical thinking about the processes discussed. Too often it just consists of unquestioningly repeating talking points based on faulty logic. Sometimes it rivals the use of "death panels" in the their scope, and this is supposed to be a technical forum. The OP actually questioned the legitimacy of what an author was saying. He was thinking for himself.

Instead of assuming, without even a cursory understanding of the scientific process they're summarily rejecting, that a popular testing approach somehow is superior to the methods used by the people who actually created the material, maybe they should be a little self reflective and do an analysis of their own process. Perhaps that is where any discrepancy rests. Maybe, just maybe some of the popular testing method's assumptions are questionable. As they say in Princess Bride, "I don't think that means what you think that means."

Steve Smith said about his link that it was an amalgamation of things, so I don't think he would be offended to hear that most of it is in error to one degree or another. He has a link to Barry Thornton's site on film speed determination. I think it would be an excellent exercise to take a critical look at that site in this thread. Break it down and question whether each claim or statement made by Thornton is accurate.

 

[brianmquinn]

What Steve said in his links was a simplified expansion and contraction technique. It works as long as you shoot a roll under similar lighting conditions.

 

[removed account4]

so a high school student, who process film in his basement
or his school's darkroom/closet has the same lab conditions, as someone who
works at a lab at kodak? ron's home field tests are "real world", or
as close to "real world" as an emulsion scientist can get ... but they are by no means
the same thing as kid processing film in parents' downstairs bathroom.

PE obviously has the knowledge and experience to know how to tweak his
development technique to match what he was doing at home with
his results at work. i don't think a high school student,
who picks up a box of tri x, and sets his k1000 to asa 400 is going to get
the same results as ron. knowing this, his teacher probably will tell him
to set his asa to 300, instead of 400.

my personal iso for every film i shoot is between 4 and 5 stops less than box speed.

 

[Stephen Benskin]

What Steve said in his links was a simplified expansion and contraction technique. It works as long as you shoot a roll under similar lighting conditions.

It is what he said, but how accurate is the statement? Should we just accept it because it's written down, or because we've heard something like it before or someone in a position of authority said it? What's wrong with questioning it and see if it holds up to scrutiny? When shopping for a camera, you ask how many megapixels. When shopping for a television, you ask LCD or plasma, 720p or 1080p. Did anyone ask if Ralph's beautifully designed graphing spreadsheet's aim LER was geared for condenser or diffusion enlargers?

From Steve's page:
Low Contrast Scene - Decrease exposure by one stop and increase development by 25%
High Contrast Scene - Increase exposure by one stop and reduce development by 15 - 25%

Take a look at the CI/Time curve showing Tri-X 135 and APX 25 135 in Xtol. The above statement wouldn't give consistent results between the two films. The rate of development or velocity constant is based on the film/developer combination and can vary greatly.

But how often do you hear about pushing and pulling based on percentages? It just gets repeated again and again with little supporting evidence and accepted without skepticism. Using percentages is no more than a rule of thumb. By simply applying a little critical analysis, a shortcoming is revealed. There are better, more accurate methods available which is an easy conclusion to come to if we just do a little critical thinking.

 

[Stephen Benskin]

my personal iso for every film i shoot is between 4 and 5 stops less than box speed.

Have you ever considered that maybe it isn't the manufacturers who are to blame?

 

[removed account4]

Have you ever considered that maybe it isn't the manufacturers who are to blame?

why would i blame a manufacturer
because discovered a better way
to expose and process my film than
was stated on the box ?

i am glad the gave me a starting point ..

 

[2F/2F]

ISO speeds are always what is stated on the box, simply by definition of ISO film speed. One organization lists standardized criteria for the ways in which they believe it is acceptable to determine film speeds (and measurements in just about any other industry you can imagine). In order for a film manufacturer to use that organization's terminology (i.e. "ISO"), film testing must be done in accordance with one of the organization's accepted methods. Notice that Delta and T-Max 3200 say "ISO" nowhere on the box. In the data sheets, however, the ISO speeds for both of these films are listed as 1000.

EIs, on the other hand, are simply numbers that you plug into your light meter to give it a factor indicative your film's sensitivity to light, by any standard of film speed determination. The meter takes the light it gathers, applies to it the factor that you have input by setting an EI, and the result is an EV. There are set shutter and aperture combinations for each EV. Some meters display the EV, and some bypass this and just give you the exposures that match that EV.

By doing your own film speed testing, you are stating that ISO's standards are not what you wish to follow, throwing them out the window, and using different criteria to determine where to set your light meter for proper exposures. What criteria these are is entirely up to you. You are searching for the EI to use to meet your own criteria for proper exposure, not the ISO speed that your film is.

IMHO, the main reason box speed used as an EI doesn't work for people is that they use directly-read in-camera meters. I find that box speed as an EI works admirably for most with incident metering or proper grey card metering.

 

[Steve Smith]

Box speed is the true speed. If you find that is not the case for you, look at your system--it isn't the film.

There are two factors involved in determining which speed works for you.

The first is compensation for errors in metering, shutter speed, etc. but also some people like to over-expose and under develop to get a bit more shadow detail.


Steve.

 

[Vaughn]

... If you think there is is a difference between the science and the "real world," you have probably misunderstood the science.

Another way of looking at it -- If you think that the science and the "real world" are identical, you have probably misunderstood the real world...and probably the science.

"Atoms are not things." Werner Heisenberg
"The universe is made up of stories, not atoms." Muriel Ruckeyser

 

[Photo Engineer]

I'll have to go back in time to when I was about 8 - 12 years old and developing my own film. If < see that? IF > I followed the manufacturers instructions for time and temperature, even though I was working in the kitchen or basement, I got the right speed and contrast. If I deviated from the box instructions, I did not. The difference today is that if I deviate from the instructions, I know what to expect and why!

PE

 

[Diapositivo]

I side with the "ISO speed is ISO speed period" crowd and I would like to offer a comparison.

In the digital domain, sometimes if you meter a scene "correctly" you find that the histogram does not arrive near the right edge of graph base. Some of the dynamic range of which the camera is capable is "wasted" by not using the part, near the highlights, where more details can be recorded.

So what the photographer does when taking pictures with a digital camera in such a situation? He intentionally overexposes the image, so that the histogram arrives "just" at the right end. This is known as the Expose to the Right technique, or ETTR. One valid explanation is given here:

http://www.luminous-landscape.com/tutorials/expose-right.shtml

Having ETTR, a photographer would not say that the real ISO sensitivity he used for the scene is different from the theoretical, or scientific, or laboratory one. He just knows that ISO sensitivity is one thing, and where you "place your highlights" is another. He places his highlights on the upper part portion of the capture range of his camera, and then he "develops" (with the raw converter) in such a way that he compensates for his "intentional mistake" (which is not a mistake) which would have caused an overexposure. He makes the most of the material he uses. He can do this because he has this second "raw conversion" step so he has an added degree of freedom with the capture step. If he had to send in real time a JPEG out of camera, and he used this ETTR technique, in this situation he would send an overexposed image. But when using raw he doesn't care if an object of 18% reflectivity does not fall into "middle grey".

Now we go back to B&W analogue photography, where I think there is some kind of "expose to the right" logic, totally analogous to the ETTR of the digital world.

Nobody uses the B&W negative "as is". You have to make it pass through a second stage, printing. So the negative is your "raw file".

You might find that, in order to have the highest detail level in the shadows, you want to place your zone I just above the foot of the negative material. Supposing that you actually want middle grey in zone V in your final print, you don't care if, so exposing, zone V in the negative does not show a middle grey, because you are going to care about this during printing. What you want, is to expose a negative that will help you in reaching the effect you want in your final print. Given this, you might find yourself "exposing to the right" your negatives.

So, saying that the film sensitivity is not the declared one, because you might have a problem with the accuracy of you shutter, or diaphragm, or lightmetre, is IMO a logical and not just a semantic mistake.
Furthermore, exposing a negative in a way that gives you, after the necessary further step of printing, a more pleasing result, can be said and practiced without questioning the exactness of the ISO speed declared for the film. The ISO speed is the ISO speed. Simply, you don't care about exposing your raw negative for having middle grey in zone V.

I personally only work with slide film. If shutter speed, diaphragms, lightmetres and film speed were not in reality what they are in the laboratory, I don't think I could expose well a slide if not by chance. I expose my slides correctly because film, diaphragm, shutter and lightmetre all behave in practice as they do in the lab. The fact that "infallibly" I obtain middle grey in zone V means that ISO speed is the "exact" value in film, the value that gives you middle grey where you expect it, on film.

Fabrizio

 

[frednewman]

Hi andysig

I've been involved with BTZS film testing for the past 20 years doing it for myself and the film testing service for The View Camera Store and have found film speed can vary depending upon many factors. Film speeds do vary depending upon the developer being used. For 400 T-Max I have found the film speed to be 400 when processed in Ilford DDX developer.

I can't figure out all the complaining about film testing when with the method Ralph Lambrecht uses and the BTZS method I use requires after the film is pre-exposed, the processing of 5 sheets of film at 5 different times (4, 5.5, 8, 11, and 16 minutes). With the BTZS film tubes thats about an hour in the darkroom. I call it doing your homework and the results are worth it when you go to print a negative.

Please see Phil Davis's article on how to read a film test:
http://www.btzs.org/Articles/HowToReadFilmTest.htm

I basically got involved in film testing out of frustration trying to print bad negatives.

Fred Newman

 

[cowanw]

Just a comment here!

Kodak has ISO certification for all of the "standards" of the industry. One ISO standard is for ISO speed! This speed is determined in the lab by direct calculations and is then VERIFIED by field experiments to be correct. All Kodak films are thus verified for speed 2 ways. If they are not, then they cannot claim the ISO label for speed. Remember that ISO is a lab defined methodology. Remember that Kodak does it BOTH ways.

When I was there, the release B&W developer was D-76 straight! All developers are tested though and posted with the data on the Kodak web site.

PE

Ron do you remember when ISO replaced ASA. The most common idea seems to be 1987 which is the date of the last ISO document but I have a publication that predates that. If anybody knows you will.

 

[Photo Engineer]

Bill;

I really don't remember. Sorry. Your date sounds about right. And, the ISO / ASA change is so slight it is really not very significant. It is on the order of 1/3 stop or less. I use old meters and new meters calibrated in both units and get just about the same answer with both of them. For example, my old Nikormat and Nikomat cameras were in ASA units and my new RZ is in ISO as is my Sekonic spot meter and they are all just about identical to within that 1/3 stop or less.

PE

 

[Diapositivo]

Ron do you remember when ISO replaced ASA. The most common idea seems to be 1987 which is the date of the last ISO document but I have a publication that predates that. If anybody knows you will.

I found this, for colour negative material there is an ISO specification dating back to 1979.

http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=11947

For what I remember, the ASA and DIN method were different so that, on rare occasions, a film could be rated let's say ASA100 but not DIN 21. It was certainly the case of a Kodak material, a negative "vericolor" professional IIRC, in the eighties or early nineties, it was rated something like ASA 160 but not DIN 23 (it was 22 or 24).

The ISO standard acquired the double notation (not "ISO 100" but "ISO 100/21", strictly speaking) but I remember having read somewhere that the ISO method substantially followed the ASA method, not the DIN one.

I think that until the advent of digital people went on saying "ASA" even if film had been marked as "ISO" for many years.

Fabrizio

 

[Sirius Glass]

I side with the "ISO speed is ISO speed period" crowd and I would like to offer a comparison.

In the digital domain, sometimes if you meter a scene "correctly" you find that the histogram does not arrive near the right edge of graph base. Some of the dynamic range of which the camera is capable is "wasted" by not using the part, near the highlights, where more details can be recorded.

So what the photographer does when taking pictures with a digital camera in such a situation? He intentionally overexposes the image, so that the histogram arrives "just" at the right end. This is known as the Expose to the Right technique, or ETTR. One valid explanation is given here:

http://www.luminous-landscape.com/tutorials/expose-right.shtml

Having ETTR, a photographer would not say that the real ISO sensitivity he used for the scene is different from the theoretical, or scientific, or laboratory one. He just knows that ISO sensitivity is one thing, and where you "place your highlights" is another. He places his highlights on the upper part portion of the capture range of his camera, and then he "develops" (with the raw converter) in such a way that he compensates for his "intentional mistake" (which is not a mistake) which would have caused an overexposure. He makes the most of the material he uses. He can do this because he has this second "raw conversion" step so he has an added degree of freedom with the capture step. If he had to send in real time a JPEG out of camera, and he used this ETTR technique, in this situation he would send an overexposed image. But when using raw he doesn't care if an object of 18% reflectivity does not fall into "middle grey".

Now we go back to B&W analogue photography, where I think there is some kind of "expose to the right" logic, totally analogous to the ETTR of the digital world.

Nobody uses the B&W negative "as is". You have to make it pass through a second stage, printing. So the negative is your "raw file".

You might find that, in order to have the highest detail level in the shadows, you want to place your zone I just above the foot of the negative material. Supposing that you actually want middle grey in zone V in your final print, you don't care if, so exposing, zone V in the negative does not show a middle grey, because you are going to care about this during printing. What you want, is to expose a negative that will help you in reaching the effect you want in your final print. Given this, you might find yourself "exposing to the right" your negatives.

So, saying that the film sensitivity is not the declared one, because you might have a problem with the accuracy of you shutter, or diaphragm, or lightmetre, is IMO a logical and not just a semantic mistake.
Furthermore, exposing a negative in a way that gives you, after the necessary further step of printing, a more pleasing result, can be said and practiced without questioning the exactness of the ISO speed declared for the film. The ISO speed is the ISO speed. Simply, you don't care about exposing your raw negative for having middle grey in zone V.

I personally only work with slide film. If shutter speed, diaphragms, lightmetres and film speed were not in reality what they are in the laboratory, I don't think I could expose well a slide if not by chance. I expose my slides correctly because film, diaphragm, shutter and lightmetre all behave in practice as they do in the lab. The fact that "infallibly" I obtain middle grey in zone V means that ISO speed is the "exact" value in film, the value that gives you middle grey where you expect it, on film.

Fabrizio

You can do all of this IF your equipment is calibrated correctly and use the ISO number! Then you do not have to waste film, chemicals and time doing endless and meaningless tests.

Film testing is a WOMBAT! [Waste Of Money Brains And Time]

Steve

 

[2F/2F]

I am curious to know if ANSI still bothers to oversee standardization for film speeds. If there is an ANSI standard, who uses it?

 

[Stephen Benskin]

Ron do you remember when ISO replaced ASA. The most common idea seems to be 1987 which is the date of the last ISO document but I have a publication that predates that. If anybody knows you will.

I'm not sure when an ISO was agreed upon, but the big change was in the 1960 standard where a fixed density point was adopted but with specific contrast parameters. This kept the precision of the US' fractional gradient method incorporated into the ease of DIN method which eliminated the major stumbling block toward creating a universal standard.

 

[Stephen Benskin]

I am curious to know if ANSI still bothers to oversee standardization for film speeds. If there is an ANSI standard, who uses it?

Home page
http://www.ansi.org/

Photo
http://webstore.ansi.org/FindStanda...=1&PageNum=0&SearchTermsArray=Photo|null|null

ISO Catalog
http://www.iso.org/iso/iso_catalogue.htm

 

[Ian Grant]

Ron do you remember when ISO replaced ASA. The most common idea seems to be 1987 which is the date of the last ISO document but I have a publication that predates that. If anybody knows you will.

ISO didn't replace ASA it incorporated it and still does, the ISO speed gives both the ASA/BS and DIN speeds.

So when we talk about the standards changing we are really referring to the ASA/BS component rather than the German DIN part.

Ian