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

[danmc]

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.

 

[Stephen Benskin]

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

 

[MattKing]

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.

 

[danmc]

@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:

 

[Doremus Scudder]

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

 

[revdoc]

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

 

[danmc]

@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!

 

[Stephen Benskin]

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.

 

[danmc]

@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.

 

[MattKing]

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

Along with:

 

[Craig]

The 1996 edition of the Xtol datasheet shows 6.5min for 400 and 7.25min for 800.

Similarly, the Tmax datsheet gives a time for 800 in Xtol as 7.25.

 

[Sirius Glass]

Welcome to Photrio!

 

[danmc]

Thanks @Sirius Glass !

 

[Stephen Benskin]

Upon reviewing the Xtol table again, the transcription error appears to be more to do with the CI than the processing time. Kodak doesn't recommend increasing development time with 400TMY when rating it at 800. The processing times for each of the development methods and temperatures has the same development time when rating it at 800 as when rating it at 400. This conforms with their recommendation. They just forgot to change for CI value for the 800 EI to 0.56. They would then probably need to change the CI values for EI 1600 and 3200. If they are using 0.56 for both 400 and 800, the other CI values need to be shifted down.

I also noticed a note on the 400TMY data sheet. It said that the T-Max films have less sensitivity to blue light than most other black and white films.

What follows is speculation. The 100TMX doesn't appear to have the same note, and it also doesn't have the same processing suggestion for EI 100 and EI 200 ratings. My first thought had to do with the development velocity of 400TMY. The time/CI charts in the data sheet didn't help. The way they are designed creates steep, straight curves which I found hard to interpret. While it may have something to do with this, it may also have something to do with the blue sensitivity. In general, black and white film tends to have a little extra blue sensitivity. When determining the ISO speed, the sensitometer color temperature is at daylight. It was changed in the 1960s from sunlight. This change required the speed constant in the speed equation to be adjusted by 1/3 stop to adjust for the increase in blue light which would have made the film appear faster than it actually is. So the 0.80 in the speed equation 0.80 / Hm compensates for the speed increase from the bluer light.

If the film doesn't have a higher blue sensitivity, the higher Kelvin wouldn't necessary affect the speed, so the 1/3 stop adjustment would rate the speed 1/3 stop slower than it actually is. Depending on the blue sensitivity, the film's response could be even less sensitive to blue, so by testing the film using the ISO Standard, an ISO 400 for 400TMY could be equivalent to an ISO 500 or 640 of other films when used in shooting conditions. If this is the case, adjusting the processing for an EI 800 wouldn't be necessary.

 

[Klaus_H]

The contradictions in the development times in documents J107 and J109 are understandable, as Kodak reformulated TMX 400 in 2002 and 2007. The fine grain was increased and the development times changed.

I have copies of document J109 from 2004, 2008, and 2018. The changed development times were included in J109 ref 3-08 from 2008. They refer to the “new” TMAX 400.

 

[Stephen Benskin]

The contradictions in the development times in documents J107 and J109 are understandable, as Kodak reformulated TMX 400 in 2002 and 2007. The fine grain was increased and the development times changed.

I have copies of document J109 from 2004, 2008, and 2018. The changed development times were included in J109 ref 3-08 from 2008. They refer to the “new” TMAX 400.

All true, but in this case the contradiction is a physical impossibility. You can't have a change in the CI without changing time, temp, agitation, or developer. My initial response was the same times for EI 400 and EI 800 were the mistake, but in the 400TMY data sheet notes, Kodak recommends keeping the development times for normal when exposing at EI 800. The Xtol data sheet reflects this, but the CIs change and this is the error. The CIs for 400TMY need to be adjusted. One option is to do what they did with EI 100 / 200 by combining them into a single row.

I found adjusting the luminance value by 2/3 of a stop per stop push gives you the aim CIs when "pushing for speed" (as opposed to 1 stop for pushing for contrast).

So if EI 400 and 800 has no change in the processing times, the CIs should be:

Of course without knowing the reason why Kodak recommends keeping the same development times for EI 400 and 800 400TMY, changing the other CIs can only be speculation. The large jump in development times between EI 800 and 1600 suggest the development times for EI 1600 and 3200 are for their stated CIs.

 

[MattKing]

Of course without knowing the reason why Kodak recommends keeping the same development times for EI 400 and 800 400TMY

Commercial reasons related to usability. The film was designed to serve users well who were having their film developed by high volume commercial processors, and didn't want to pay for higher cost push development.
In addition, I think the positive effects on shadow rendition of increasing development of one stop under-exposed TMY-2 are, relatively speaking, of less weight than the negative effects on highlight rendition. That, of course, is as much a preference/subjective factor as an objective one, but if the target user is making photographs of lighter skinned people and other subjects with lots of mid-tones and highlights, it makes sense.
That happens to match my preference.

 

[Doremus Scudder]

Well, either the developing time is wrong for E.I. 800, or the C.I. numbers are wrong for both E.I. 400 and 800.

What is fairly clear and logical is that you can't and won't get an increased C.I. for the same developing time, even with the film speed rated differently.

Doremus

 

[RalphLambrecht]

@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.

let's discuss this interesting subject a bit longer before we close it out. I read all the arguments against the idea that exposure changes CI, but don't we know from experience that it really does? Less exposure results in a thinner negative when the other processing variables remain the same. And a thinner negative needs a different paper grade to make a successful print. Doesn't that indicate a different negative CI?

 

[RalphLambrecht]

After thinking about this a bit more, I'm now convinced that exposure changes CI. It doesn't just create a thinner negative. It also makes us print a different portion of the curve:
's characteristic curve you're using.

The film's characteristic curve has different slopes in different regions:

• Toe (shadow region)—lower slope, less contrast
• Straight-line portion—consistent slope (this is where CI is measured)
• Shoulder (highlights)—slope decreases again

When we underexpose:

• We're pushing more of your tonal range into the toe region, where the curve is flatter
• This effectively gives you lower contrast in practice
• Hence why we need a harder paper grade

When we overexpose:

• More of your range sits in the straight-line portion or even into the shoulder
• The effective contrast of the usable negative can appear higher
• We might need a softer paper grade

So while the CI (measured at a specific density range) remains constant for a given development, the effective working contrast of our negative changes because exposure determines which section of the characteristic curve we're utilizing.


In that sense, exposure does affect practical negative contrast!

 

[Stephen Benskin]

After thinking about this a bit more, I'm now convinced that exposure changes CI. It doesn't just create a thinner negative. It also makes us print a different portion of the curve:
's characteristic curve you're using.

The film's characteristic curve has different slopes in different regions:

• Toe (shadow region)—lower slope, less contrast
• Straight-line portion—consistent slope (this is where CI is measured)
• Shoulder (highlights)—slope decreases again

When we underexpose:

• We're pushing more of your tonal range into the toe region, where the curve is flatter
• This effectively gives you lower contrast in practice
• Hence why we need a harder paper grade

When we overexpose:

• More of your range sits in the straight-line portion or even into the shoulder
• The effective contrast of the usable negative can appear higher
• We might need a softer paper grade

So while the CI (measured at a specific density range) remains constant for a given development, the effective working contrast of our negative changes because exposure determines which section of the characteristic curve we're utilizing.


In that sense, exposure does affect practical negative contrast!

It changes the negative density range and relationships between the densities on the negative as compared to the Luminance values from the original scene. The characteristic curve is a graphic representation of a sensitometric test of a film under specific conditions. It is fixed as long as those conditions are maintained. Camera exposure can be considered to then fall on that curve. I like to think of it as being superimposed onto the curve. Luminance range and exposure placement will determine the resulting densities from the camera illuminance. The relationship between the Luminance's from the original scene and the resulting print reflection density can be seen in the tone reproduction curve on a tone reproduction diagram. This of course, includes other factors such as flare, paper choice, and paper LER. I don't believe this is just a debate about semantics. It's about a fundamental perception of the process.

This example has the same luminance range but different camera exposures.

The next example is of a short luminance range.