Scientific reason why some developers causes decrease film speed

[Paul Ron]

bill, thanks for the article. to download it you have to go to this link...
https://sci-hub.hkvisa.net/10.1117/12.933997#

[esearing]

One more on the topic of "film speed".


"Executive Summary: Almost everyone who does rigorous film testing ends up shooting at roughly one f/stop slower than box speed for normal development: 200 for HP5+ and TMY, 50 for FP4+ and TMX, etc. The more important issue is determining the development times which work for you. Even then, if your results are substantially different from others, you're probably doing something wrong."

Why?
Bernice

Because teachers have told the newbies to do so , then they continue to use the practice years after learning it. Corran and I once had a conversation about the treatment of FP4+ . He meters it at EI 64 or 80 but I set my meter to 100 for convenience. he puts his shadows at Zone 2 whereas I often put my shadows at zone 3 so our net exposure is somewhat the same or within 1/2 a stop. He uses Pyrocat HD at full strength for multiple sheets, but I use pyrocat-M diluted and longer processing times one sheet at a time. So placement of your tones has an effect , how you develop for time/contrast has an effect, then ultimately scan/paper choices have an effect. We all are taught to standardize these things but knowing when to deviate from the norm and experimenting is what makes photography as a craft more interesting. I think the accidents, failures, and mis-steps are also good teachers of what will and won't work in our practice. There is also a difference in need for consistency between commercial work for clients versus work for personal pleasure/artistry.

[LabRat]

Because teachers have told the newbies to do so , then they continue to use the practice years after learning it. Corran and I once had a conversation about the treatment of FP4+ . He meters it at EI 64 or 80 but I set my meter to 100 for convenience. he puts his shadows at Zone 2 whereas I often put my shadows at zone 3 so our net exposure is somewhat the same or within 1/2 a stop. He uses Pyrocat HD at full strength for multiple sheets, but I use pyrocat-M diluted and longer processing times one sheet at a time. So placement of your tones has an effect , how you develop for time/contrast has an effect, then ultimately scan/paper choices have an effect. We all are taught to standardize these things but knowing when to deviate from the norm and experimenting is what makes photography as a craft more interesting. I think the accidents, failures, and mis-steps are also good teachers of what will and won't work in our practice. There is also a difference in need for consistency between commercial work for clients versus work for personal pleasure/artistry.

You need a center baseline for your exposures... Its like levels... You know where your shadows will fall, and the highlight you can hold... You will know where it will land on your paper (with your process)...

Then creative control comes in to raise/lower the key of your scene, but can measure the extremes of the scene and decide how much/little is enough for those areas...

If you are calibrated, you know what you can get away with (or not)...

Steve K