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.