True ISO Chart

[ChrisP]

Is there anywhere on the internet that has a chart of true ISO values, or at least ISO values relative to one another in a common developer.

And on the same note, is there anywhere that shows the increase in speed a developer gives different films relative to other developers.

I know true ISO is hard to agree on but, it shouldn't be too bad to find ISO values of films relative to eachother if they're developed the same way right?

I'm just curious about this more than anything, not trying to start a big "true ISO" technical debate.

Thanks,
Chris

 

[Chriscrawfordphoto]

The speed you should expose film at depends on the developer. So there is no 'true ISO' chart. There are so many developers out there that it really depends on the chemicals you choose to use. Speed is one thing that developer choice affects. Others are grain, sharpness, contrast and gradation. You choose a developer that gives the characteristics you want, and you usually can't have everything!

Look at the tech info pages on my website. i've got a chart of tested speeds and developing times for a lot of films i have used. Of course, your speed may still vary from mine, despite my rigorous scientific testing. My light meters are all calibrated to match each other precisely and they are perfectly accurate. Yours may not be.

 

[Pirate]

Interesting topic, I've not looked at it from this angle before.

 

[jan normandale]

If you don't want to "..start a big "true ISO" technical debate." just go to Massive Dev Chart and do some interpolations. That will help you get "close" to some of the emulations you're looking for. There's more data there in one place than anywhere else that I know of on the topic of developers and films.

Let us know what you discover and good luck!

http://www.digitaltruth.com/devchart.php

BTW & FWIW, Chris' charts are very good....

 

[Roger Hicks]

Many people are perfectly happy setting the box speed on their meters, and if you're not, well, what does true ISO speed matter? You want an EI. Jan's advice is excellent, or alternatively, use the rule of thumb that no speed increasing developer gives a full stop of extra speed over (say) D76, though some come close, and that as long as you avoid faddish developers, most ultra-fine-grain formulations lose about the same amount of speed as speed increasing developers gain, i.e. 2/3 stop to 1 stop. Thus, FP4 goes from about 80 to about 200, depending on developer, while HP5 goes from about 250 to 650+.

ISO speeds are not hard to understand or agree, which means that true ISO speeds are not hard to understand or agree. Anyone with the right equipment can test true ISO speed in any developer.

Second, as Chris says, ISO varies with developer, and any developer can be used as long as the manufacturer says what it was. This is how Fomapan 200 is marketed as an ISO 200 film, even though its speed in any given developer is just about identical to Ilford FP4 Plus. THe 'ISO 200' claim is in a Foma speed increasing developer.

Anyone can establish useful personal EIs, and, if they have a densitometer and sufficient patience, compare different films by plotting D/log E curves, but this is NOT the same as determining 'true ISO'.

I have done comparisons, thereby (for example) confirming the information I had already got from Foma spec sheets about my suspicion that Fomapan 200 and Ilford FP4 Plus are very similar in speed, but I can't do ISO determinations, nor is there any reason why I should. After all, all I care about is the best EI for my own use, and the manufacturer's stated ISO standard is the best starting point for this -- certainly, far better than the vapourings of any self-appointed internet expert.

Cheers,

R.

 

[charjohncarter]

I'd like to see charts like that, AND H-D curve charts for different films and developers. Which is related to ISO determination.

 

[ChrisP]

Thanks for the info everyone. And I like your site "other Chris" you've got some nice stuff on there

 

[Roger Hicks]

One other point about EIs is that it depends on your metering technique and subject matter. Use the shadow index on a spot meter and you will be best served by a speed close to the actual ISO. With a broad-area meter, you can double the film speed on a misty day and halve it on a sunny day.

Cheers,

R.

 

[Inprogress]

Oh wonderful, just when I thought I should just develop my own film I read this about developer affecting ISO speed? Am I understanding this correctly? Or are we...ergm you guys talking about speed in reference to the variance in the development time of a specific brand/type/ISO film?

Sorry for the question, newbie in the more technical aspects of film photography - guy who wants to move to MF in the near future and who, given his town, will need to read up on all the aspects of developing film - especially on a budget at home.

 

[Roger Hicks]

Oh wonderful, just when I thought I should just develop my own film I read this about developer affecting ISO speed? Am I understanding this correctly? Or are we...ergm you guys talking about speed in reference to the variance in the development time of a specific brand/type/ISO film?

The manufacturers' spec sheets tell you most of what you need to know. "Speed increasing' developers typically give you 2/3 stop extra speed (400>650) with coarser grain and 'ultra fine grain' developers typically give you 2/3 stop less (400>250) with finer grain.

A true ISO speed specifies a certain level of shadow detail and a certain contrast. As soon as you give more or less development than required to meet ISO conditions, you are no longer talking about ISO speeds but EIs (exposure indices).

To learn more about ISO speeds, read: http://www.rogerandfrances.com/subscription/ps iso speeds.html

For more about development technique, try: http://www.rogerandfrances.com/subscription/ps neg development 1.html

Finally, remember that the penalties for overexposure are far less severe than the penalties for overexposure, and that many people deliberately overexpose, whether because they're not that clear on how to meter or because they prefer the tonality.

Cheers,

R.

 

[charjohncarter]

Kodak does list the ISOs for different (of their) developers. Probably Ilford does too.