Kodax XTOL datasheet: Increased CI without increase in development time. How?

Hi All, First time posting to this forum, so I'm hoping I'm asking this in the right place. Let me know if not. I've been taking a deep dive in understanding the nuances of development with XTOL and T-Max 400. One thing I cannot understand from the XTOL data sheet is that they show contrast index increasing for push processing of 1 stop without an increase in development time. This does not agree with my experience or understanding of development. How can the contrast increase if the development time, temperature and agitations are the same? Is this a mistake in the datasheet or am I missing something? Just reducing exposure should not increase contrast index I wouldn't think. Thanks in advance for any insights.

Looks like a transcription error. Tables are notoriously error prone.

It is probably related to the design of the T-Max films - in particular T-Max 400.
One of the design goals being that the film can be exposed at EIs of either 400 or 800, and developed for the same time, while still give giving commercially acceptable results. If I understand the method for measuring CI correctly - a big if - the deemed acceptable loss of shadow detail resulting from using an EI of 800 will result in a different set of measurement points on the characteristic curve of the test film - thus leading to a different measured CI. @Stephen Benskin understands such things much better than I do.

@Stephen Benskin I'm guessing you are likely right. They do say in several places to "use normal processing for one stop push" so I'm guessing the time is not a typo, but the CI should have been 0.56 for both. Although I don't think the time is right either, I find that I need a decent amount more time to reach the CI's in this table for XTOL. E.g., I can consistently get 0.58 CI with 7 minutes at 23C using Kodak's recommended agitation in a small tank. At 20C it is significantly longer. Thanks for helping confirm I'm not crazy.

@MattKing Could be, but that doesn't agree with my reading of the Kodak Sensitometry Workbook, from that the CI measurement is strictly a function of the H-D curve which won't vary based on how you shoot the film (EI).

For ref, here are the curves from my tests with the CI slope lines using the 0.2 and 2.2 points:

Every other set of development times in the chart has a progression of times getting proportionally longer for greater C.I. I imagine that the 6 1/2 minutes for E.I. 800 and C.I. of 0.62 is simply an error. It looks like it should be around 7 1/4 minutes if you split the difference between the values above and below it.

Best,

Doremus

From my copy of the Xtol data sheet for small tank development, publication J-107:

@revdoc that makes more sense. Proof that newer isn't always better! I'm using J-109 from 2018. I still think the times are way too short, but that is probably a discussion for another thread. Thanks!

Notice the difference of the CI for normal between the two data sheets. The older version uses a CI of 0.58 and the new uses CI 0.56. It's a question of which value for flare they chose. In the late 80s and early 90s, Kodak started using CI 0.58. I believe it's because of the greater use of small format cameras with lenses containing more lens elements. It looks like they went back to the previous version of CI. Interesting enough, the Xtol datasheet for non-Kodak films still uses CI 0.58 for normal. Probably because no one wanted to spend the money to retest. The difference is 0.56 uses a value of 0.30 to 0.34 and 0.58 uses 0.40 for flare.

The recommendation for not changing development with a one stop adjustment in EI has to do with exposure and latitude. CI is an indication of gradient and you need to change either time, temp, agitation, or chemistry to change the CI.

@Stephen Benskin My guess is that at some revision of the J-109 they had two different times for one stop push and the contrast index change was correct at that point, but they changed their recommendation on the dev time but didn't update the CI in the table. Thanks for confirming my understanding that EI cannot affect CI.

FWIW, from the most recent Kodak Alaris datasheet for T-Max 400:



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