Speed difference between Acros II, TMX, and Delta 100 at same CI?

Stephen Benskin · 2026-03-03T07:46:15-0500

Bill Burk said:
Process promptly?

I have several studies that show significant speed differences between fresh exposure and film that has sat for several months between exposure and processing.

The test is straightforward. I put a sensitometric exposure on every other roll of film I roll as I load the cassette.

Then before processing I pull a strip of film from the loader and put a fresh sensitometric exposure on it.

Process in the same tank for the same time, I get two completely different contrast indexes and speeds.

The obvious lesson is: Process promptly.

Then you get the most speed and contrast.

The corollary is: give greater exposure and process to higher contrast index if you feel like you might delay processing

Bill Burk said:
Process promptly?

I have several studies that show significant speed differences between fresh exposure and film that has sat for several months between exposure and processing.

The test is straightforward. I put a sensitometric exposure on every other roll of film I roll as I load the cassette.

Then before processing I pull a strip of film from the loader and put a fresh sensitometric exposure on it.

Process in the same tank for the same time, I get two completely different contrast indexes and speeds.

The obvious lesson is: Process promptly.

Then you get the most speed and contrast.

The corollary is: give greater exposure and process to higher contrast index if you feel like you might delay processing.

It's part of latent image keeping. ISO 6 has it in 5.4.1 Conditioning of specimens. "The processing shall be completed in not less than 5 days and not more than 10 days after exposure for general purpose films, and not less than 4 hours and not more than 7 days after exposure for professional films." The old standard had a hold time longer than 2 hours as the effect tends to plateau after a few hours. The standard also stipulates the samples be kept at 23oC +- 2oC at a relative humidity of (50 +- 5)%.

Keith Tapscott. · 2026-03-03T11:04:14-0500

Craig said:
Makes sense, Perceptol typically loses a stop in speed, give or take.

He may have gone over to digital imaging now.
I think he used a mamiya rb 67 and a Sinar F 4x5.
The latter he used FP4 Plus at a low ISO rating of around E.I.32-40, again he used diluted Perceptol.

DREW WILEY · 2026-03-03T11:08:31-0500

Pan F was designed to accommodate about the same luminance range as color slide film. Yeah, you can tweak the contrast a little during development, but it does best when you seek out subject matter of limited brightness range, or else artificially illuminate it in that manner.

The best developer for Pan F I've used is a special tweak of PMK pyro, rating the film at 25. It's not a particularly versatile film, so I seldom shoot it. But I do have a good number of superb prints made from Pan F 120. It has its own special look.

Acros is quite different, even in spectral sensitivity. Too bad it's no longer available in sheets.

Speed difference between Acros II, TMX, and Delta 100 at same CI?

Stephen Benskin

Keith Tapscott.

DREW WILEY

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