BTZS / TMAX / XTOL 1:1 Film Density Test Question

[mpålsson]

Dear All,

Over the past few months, I’ve been slowly working my way through Phil Davis’s Beyond The Zone System. Recently, I’ve completed a few film density tests according to his instructions in Chapter 6. I used BTZS tubes to develop TMAX 100 sheet film (exposed under my enlarger’s light in a contact printer with a Stouffer 4x5 step wedge) in XTOL 1:1 at 20C.

I developed the first set of sheets at 5’35”, 6’45”, 8’, 9’30”, and 11’15”. But these times were evidently too short as all the curves were too flat to correctly position the ISO triangle on the 0.1+BF IDmin line. So, I ran a second test with longer times (9’30”, 11’15”, 13’30”, 16’). This time I was able to position the ISO triangle on the IDmin line correctly, and it came out to be very close to the 13’30” curve.

Overall, I’m a bit surprised. Before reading the book, I just developed the film according to Kodak’s data sheet, which recommended 9’45” for sheet film processed in rotary tubes with XTOL 1:1 at 20C. As I recall, Kodak says their normal processing times yield a contrast gradient of something like 0.56. But according to my most recent test, the same time would only yield a contrast gradient slightly over 0.36.

Another point of intrigue is why the curves don’t accelerate upward parabolically as the book’s examples appear, but instead seem to be flattening out, or at least stabilize linearly at a lower gradient in the highlights than the mid-tones. I’ve attached my hand-plotted chart below.

So I’ve decided to reach out to the community hoping someone might share their experience. Have I done something wrong in my tests, or do my results seem reasonably accurate? Why such a difference then between Kodak’s recommendations and my tests? I guess I might not have been agitating the film as intensely as Kodak expects, but I felt like I was always agitated the film pretty decently, keeping all the tubes rolling constantly throughout. Anyway, anyone who could offer some advice or share their experience would be most appreciative!

[bmikiten]

Hi...

TMX commonly has that shape which is why you can move exposure up and down the curve. It is common with some developers that you have to change dilution especially at lower volumes (60ml) in order to get more activity and a steeper curve. As curves get closer together with longer development times you can use this as an indicator of this issue. If you'll send me your step wedge readings and the film readings, I'll put them into the film plotter software and check your numbers.

Brian

[Michael R]

The shape of the curve looks normal to me. It is largely because that is what the TMX 100 curve does. If you look at the attached (bottom section for TMX) you can see XTOL is only slightly different than D-76. As for development time, I don’t use BTZS tubes but my times are also longer than Kodak indicates for TMX (also TMY-2 but to a lesser degree).

[mpålsson]

Hi...

TMX commonly has that shape which is why you can move exposure up and down the curve. It is common with some developers that you have to change dilution especially at lower volumes (60ml) in order to get more activity and a steeper curve. As curves get closer together with longer development times you can use this as an indicator of this issue. If you'll send me your step wedge readings and the film readings, I'll put them into the film plotter software and check your numbers.

Brian

Brian,

Thank you so much for your reply and offer! That's all very interesting. And may I send you a PM with the data? Is an Excel spreadsheet okay? Thank you so much again!!

[mpålsson]

The shape of the curve looks normal to me. It is largely because that is what the TMX 100 curve does. If you look at the attached (bottom section for TMX) you can see XTOL is only slightly different than D-76. As for development time, I don’t use BTZS tubes but my times are also longer than Kodak indicates for TMX (also TMY-2 but to a lesser degree).

Thank you so much, Michael, for sharing this! It is very interesting to see, and I feel a bit of relief already.

[Bill Burk]

mpålsson,

You say you saw: "ISO triangle came out to be very close to the 13’30” curve"

That's the developing time I get when I meet the ISO triangle for TMAX 100, TMY2 and TRI-X in D-76 1:1. So your times are exactly the same as mine.

For 4x5 I tray develop, shuffling constantly. For tanks, I agitate the Kodak way (invert a few times every 30 seconds).

I want to share a criticism of BTZS (or refinement if you accept). The EI fluctuations that BTZS recommends are based on observation that the 0.10 density above base+fog moves in relation to the exposure scale with different development times. BTZS concludes that the effective speed of film has varied, thus they conclude that you should respond by varying exposure.

Instead of changing the EI in the field for each sheet, I recommend that you adopt the full rated (box) speed of the film for incident metering, and reduce speed 2/3 stop beneath rated film speed when determining exposure by Spot metering (Zone System read spot and place on a shadow Zone).

I have had long discussions with Stephen Benskin about this and there is a history that the speed point 0.10 was selected because it is easy to find on graphs. It's not really the speed point. The actual speed point (determined by Loyd Jones experiments with thousands of prints judged by people) is at the point where the toe curves to about a third of average gradient.

That third of average doesn't move around very much with changes in development.

There's something called Delta-X that I follow instead of latching onto that 0.10 speed that fluctuates wildly.

In brief, 0.10 speed equals Delta-X speed when the curve meets the ISO triangle. But for developing times above and below, the Delta-X speed doesn't fluctuate much with development time.

Your graph by hand is a thing of beauty. If you would like to share all your numbers (the density readings of the step wedge patches for each developing time), I could graph for you on my paper and show how the Delta-X speeds overlay works.

[Michael R]

This is true. Stephen's Delta-X paper is a good one for the newcomer, showing how the Delta-X criterion is "hiding in plain sight" within the ISO standard. The ISO triangle can be viewed as a special case of Delta-X with 0.1D as a "marker".

The nice thing in Stephen's paper is it summarizes how rather than being some sort of esoteric laboratory thing (which people often assume after learning the Zone System(s)), ISO speed is rooted in print quality. The lineage in a nutshell was:

Print judgement speed (first excellent print studies) led to Fractional gradient ("0.3G") speed (by correlation), which led to Delta-X (simpler method for estimating fractional gradient speed), leading to ISO speed

They key point in all of this is the recognition that a single fixed density (0.1D for example) on its own tells you little about how shadows will be recorded/rendered. It's contrast (ie the shadow gradient) that counts, and the relationship between shadow contrast and average contrast in the rest of the curve.

mpålsson,

You say you saw: "ISO triangle came out to be very close to the 13’30” curve"

That's the developing time I get when I meet the ISO triangle for TMAX 100, TMY2 and TRI-X in D-76 1:1. So your times are exactly the same as mine.

For 4x5 I tray develop, shuffling constantly. For tanks, I agitate the Kodak way (invert a few times every 30 seconds).

I want to share a criticism of BTZS (or refinement if you accept). The EI fluctuations that BTZS recommends are based on observation that the 0.10 density above base+fog moves in relation to the exposure scale with different development times. BTZS concludes that the effective speed of film has varied, thus they conclude that you should respond by varying exposure.

Instead of changing the EI in the field for each sheet, I recommend that you adopt the full rated (box) speed of the film for incident metering, and reduce speed 2/3 stop beneath rated film speed when determining exposure by Spot metering (Zone System read spot and place on a shadow Zone).

I have had long discussions with Stephen Benskin about this and there is a history that the speed point 0.10 was selected because it is easy to find on graphs. It's not really the speed point. The actual speed point (determined by Loyd Jones experiments with thousands of prints judged by people) is at the point where the toe curves to about a third of average gradient.

That third of average doesn't move around very much with changes in development.

There's something called Delta-X that I follow instead of latching onto that 0.10 speed that fluctuates wildly.

In brief, 0.10 speed equals Delta-X speed when the curve meets the ISO triangle. But for developing times above and below, the Delta-X speed doesn't fluctuate much with development time.

Your graph by hand is a thing of beauty. If you would like to share all your numbers (the density readings of the step wedge patches for each developing time), I could graph for you on my paper and show how the Delta-X speeds overlay works.

[mpålsson]

mpålsson,

You say you saw: "ISO triangle came out to be very close to the 13’30” curve"

That's the developing time I get when I meet the ISO triangle for TMAX 100, TMY2 and TRI-X in D-76 1:1. So your times are exactly the same as mine.

For 4x5 I tray develop, shuffling constantly. For tanks, I agitate the Kodak way (invert a few times every 30 seconds).

I want to share a criticism of BTZS (or refinement if you accept). The EI fluctuations that BTZS recommends are based on observation that the 0.10 density above base+fog moves in relation to the exposure scale with different development times. BTZS concludes that the effective speed of film has varied, thus they conclude that you should respond by varying exposure.

Instead of changing the EI in the field for each sheet, I recommend that you adopt the full rated (box) speed of the film for incident metering, and reduce speed 2/3 stop beneath rated film speed when determining exposure by Spot metering (Zone System read spot and place on a shadow Zone).

I have had long discussions with Stephen Benskin about this and there is a history that the speed point 0.10 was selected because it is easy to find on graphs. It's not really the speed point. The actual speed point (determined by Loyd Jones experiments with thousands of prints judged by people) is at the point where the toe curves to about a third of average gradient.

That third of average doesn't move around very much with changes in development.

There's something called Delta-X that I follow instead of latching onto that 0.10 speed that fluctuates wildly.

In brief, 0.10 speed equals Delta-X speed when the curve meets the ISO triangle. But for developing times above and below, the Delta-X speed doesn't fluctuate much with development time.

Your graph by hand is a thing of beauty. If you would like to share all your numbers (the density readings of the step wedge patches for each developing time), I could graph for you on my paper and show how the Delta-X speeds overlay works.

Bill, thank you so much for your insight about the ISO triangle and fluctuations in EI. I'll look into that further.

Since I'm unable to attach an Excel spreadsheet to a PM or public post, I've uploaded it to my Google drive and am sharing the link directly below.

TMX-100 XTOL 1:1 Film Density Test

All the values were recorded having zeroed my Heiland densitometer on its opal aperture. The B+F is recorded separately for each film (taken where a brown paper mask covered the edge of the film during exposure) and the density values of the steps include B+F.

Last night I also found the BTZS Plotter program online, downloaded it, and ran it with my data. I also compared my data against the sample curves for TMX developed in XTOL 1:1 (albeit at 70F, not 68F) and was somewhat surprised by the stark differences in them. I'm including a screenshot of the two side by side. (Mine is on the left, the sample curve on the right. There is a slight problem with the ISO labels, which I fixed after deleting the “personal speed point.”)



It seems my film starts to gain sensitivity at a much lower threshold, much more to the left of the x-axis than the sample file shows, but the contrast is also much lower and never achieves the same height in the highlights.

I'm also curious about how the Plotter calculates the B+F of the film. I never inputted those values, and there doesn't seem any way to input them manually. How does it come up with these numbers? Especially since they are different than the B+F that I measure with my densitometer.

I'm not sure if it makes any difference, but are you supposed to input the film density values with or without B+F? The data in the sample file seems like B+F was subtracted from the density readings, as the lowest curve values are often 0.01, much lower than the B+F of most film stocks.

[bmikiten]

Brian,

Thank you so much for your reply and offer! That's all very interesting. And may I send you a PM with the data? Is an Excel spreadsheet okay? Thank you so much again!!

Sure. An Excel sheet works.

Thanks

Brian

[Bill Burk]

Thanks! Got the data from your spreadsheet! I like to remove B+F when graphing, but BTZS wants you to include it. Ralph Lambrecht also has a spreadsheet to accompany Way Beyond Monochrome which is worth trying.