What is YOUR Usable EI – Exposure Index?

First a quick bit of background info:

Exposure Index- “EI”- is your personal speed setting for a particular film and developer combo that in most cases is different than the manufacturers posted ISO or ASA data (lots of reasons for this difference) and it reflects a photographer’s specific film requirements with regards to shadow and highlight detail, contrast, grain, etc… Many photographers do extensive testing to determine the best EI for a particular film and developer combo but in the end most photographers settle for a single EI and developer time for a particular film. An example would be- “I shoot Kodak TX at an EI of 1250 and process in Diafine 3+3 at 70F.”

Now for the Diafine Twist:

That tested EI is not the “only perfect EI” but rather just one possible working EI when using Diafine Developer. For example, I have determined that TX processed in Diafine at 3+3 has a USABLE EI range of 400-1250/ 1600…that means that I can rate it at 400 or I can rate it at 1250 if I need to or I can rate it at any in between EI based on subject exposure requirements- there is enough latitude with regards to exposure and development with TX and Diafine that both of these EI are possible for scanning purposes and produce brillant negatives…even one shot right after another on the same roll at a different EI, each would get the same processing time in Diafine– it is like working with the very forgiving Ilford XP2 Super which can handle a range from EI 100-800 (C-41 film) but with real B&W film! (Note: I love XP2 Super but it is a very different looking beast than conventional B&W film.)  With a “normal” developer, say D-76, you would need to increase or decrease your development time or temp or both if you changed your EI beyond half a stop with most black and white films.

So here are a few films I use with their USABLE EI range based on my testing. (NOTE: all USABLE EI listed are for Diafine Processing as outlined here on Figital Revolution.)

  • TX: 400-1250/ 1600 (3+3 at 70F)
  • 125PX: 125-400 (3+3 at 70F)
  • Fuji Acros: 100-200 (4.5 + 4.5 at 70F)
  • TMY-2: 400-640 (3+3 at 70F)
  • FP4+: 100-225 (3+3 at 70F)

Final Thought…why would you want to have a different EI for the same film or know the EI range for a particular film? The answer is flexability (how much can I over or under expose and still get a good negative)- with this approach and knowledge let’s say, for example, I am working with a film like Kodak TX-just load a roll in the morning and start shooting and adjust your USABLE or “flexible” EI as the day and lighting change… when you’re done just process the whole roll with your normal Diafine processing time and scan away! The results are consistantly USABLE and amazing.

9 thoughts on “What is YOUR Usable EI – Exposure Index?

  1. Thanks for this info, I’ve been experimenting with Diafine myself because I think it’s easier to get consistent results. I have tried it with Fuji Neopan 1600 @ 800 but the results were not as compelling as TX400 @1600. I will be trying Acros asap.

  2. “for example, I am working with a film like Kodak TX-just load a roll in the morning and start shooting and adjust your USABLE or “flexible” EI as the day and lighting change”

    Whoa, am I reading this right? I load 400TX in my camera. Then for early dawn shots I use the camera as if I had 800 or 1250 in it, during daylight I use the camera as if I had 400 in it, and in the home at night with available light I use the camera again as if it was 800 or 1250 once again? In other words, I have tremendous flexibility with shutter speed and aperture because the film/developer combo has such latitude?

  3. I have never used Diafine before and I scan my 35mm film using the Nikon LS9000.I will be trying your procedure real soon. My question (to be sure) is (3+3 at 70F)mean 3 minutes in Part A and 3 minutes in Part B? I don’t want to assume the Obvious

  4. Stephen

    I developed some diafine last night at 5 + 5. I didn’t check the temp, but it would have been around 25 degrees. You state 70 degrees (F) in your post’s above, but how critical is the temp? I was not that pleased with the results, particularly for the outside mid afternoon shots. they were very contrasty, and didn’t look as nice as my last few Acris rolls that I have shot. I can only put it donw to temp, but I didn’t think that it was that critical with this developer.

    1. While it is true that the temp is not critical for Diafine… it is somewhat critical for your emulsion… I suggest around 70-75 F as the best… anything under 70F in my opinion is too cold. Also agitation is very important …. please watch my videos on the proper technique.


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