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Photo Engineer
05-03-2012, 07:20 PM
John;

In the R&D process for a new developer, the researcher must be aware of speed, grain and sharpness criteria for any film. The contrast is generally built into the film and is considered to be a constant to be attained. In negative films, that value is generally a value of 0.6 - 0.8. The lower figure is for professional films and the higher value is for consumer use with relatively high flare camera lenses.

So, we have speed, grain and sharpness to work with. Only two can be improved upon at one time. Generally, we try to keep the speed up to a given specification. Therefore, new developers are made to optimize grain and sharpness. Using this as your guidelines, it is possible to design two developers that give the same speed and contrast which is essentially what Mark Overton has shown us above. These results are so close as to be indistinguishable. Only multiple runs will iron out real from statistical variations. Anyhow, these examples will probably differ substantially (or maybe not at all) in grain and sharpness.

This is the classic case of having something we think is a good new developer, but without all of the data, we cannot make a final decision. We need more data.

PE

albada
05-06-2012, 09:32 PM
Remember that experiment last week that seemed to show that Phenidone is more active at low pH than DimezoneS?
Well, I re-ran it, but changed the pH to 8.25 for both tests. Here's the one-litre formula:

Potassium sulfite 45% solution ..... 126 g
Sodium metaborate 4 mol ............. 3.4 g (was 1.93 g for pH=8.00)
Ascorbic Acid ................................. 5.5 g
Phenidone / Dimezone S .............. 0.05 g / 0.10 g

pH=8.25, TMY2: 10.5 minutes at 20C.

Here are the same curves for pH=8.00 on the left, and the new curves for pH=8.25 on the right:

50615 - 50616

The new curves (at pH 8.25) are almost identical.

However, the Dimezone/Phenidone ratio is 2.0 for all these. In other PC developers I've seen, Phenidone is typically 0.15 g/L whereas Dimezone S is typically 0.20 g/L. That's a ratio of 1.33, which is well below my 2.0.

I have a shutterspeed tester, so I measured my OM-1. At 1/30 sec, I measured speeds at the left and right sides of the film-aperture. The worst variation would cause a density-difference of 0.053 in the linear region. The curves on the left have a difference of 0.11, so I doubt it's due to the camera's variation. This makes me think Dimezone S really is more sensitive to pH than Phenidone. As usual, more tests would answer that conclusively.

Finally, XTOL uses Dimezone S at pH=8.25, so here's a comparison:

50620

These are almost identical, giving me some confidence that the high ratio above isn't due to my own screw-up involving Dimezone S.

Now what do I do? I think I'll go back to creating a concentrate that gives XTOL-like quality...

Mark Overton

Photo Engineer
05-06-2012, 10:24 PM
Well, you covered speed, but how about grain and sharpness?

PE

albada
05-07-2012, 12:52 AM
Well, you covered speed, but how about grain and sharpness?

I took the easy way out and ignored them. :)
Mostly, I was wondering about the sensitivity of these developers to low pH. At pH 8.00, even twice as much Dimezone S still does not reach the density of Phenidone. At pH 8.25, their densities are equal, but why is twice as much needed? I dunno...

Mark Overton

albada
05-13-2012, 07:31 PM
Ryuji said that he dropped the pH of DS-10 to 8.0 to improve grain. And I've heard elsewhere that reducing pH helps. So I figured I'd run a test. I dev'd a strip using each of the following five developers which cover pH 8.00 up to 8.45. Here are the 1-litre formulae:

Sodium sulfite ............................ 90 g
Ascorbic acid ............................. 9 g
Sodium metaborate ................... 4.1 / 5.3 / 5.8 / 6.4 / 7.2 g
Dimezone S ............................... 0.2 g

pH Values .................................. 8.00 / 8.15 / 8.25 / 8.35 / 8.45
Times for TMY2 ......................... 8.67 / 7.50 / 6.75 / 6.17 / 5.58 minutes

I also developed a strip in XTOL (stock) under identical conditions (20 degrees C, same agitation). Using the densitometer, I verified that the curves of all these strips were reasonably close.

The result: The grain in all these look the same!
I compared grain using a pair of 22X loupes on the light-table, moving quickly from one to the other. All look identical to me.

I conclude that with high-sulfite PC-type developers (such as XTOL), pH has negligible effect on image-quality within this range. So we might as well select pH based on other criteria, such as convenient development-times. XTOL's pH is 8.25 (I measured two batches), and that gives dev-times from 5.25 to 8.5 minutes in the MDC. Those are convenient times, so I might as well stay at 8.25 for my concentrate.

Mark Overton

Photo Engineer
05-13-2012, 07:34 PM
Mark;

Both the pH and the buffer capacity of those solutions change. You may also include ionic strength in that change. So, by making one ostensible change, you have actually made 3.

Also, without contrast comparisons, it is hard to judge grain. And, you have to consider sharpness, which may have gone down due to decreasing edge effects.

PE

albada
05-13-2012, 11:01 PM
Mark; Both the pH and the buffer capacity of those solutions change. You may also include ionic strength in that change. So, by making one ostensible change, you have actually made 3.
Also, without contrast comparisons, it is hard to judge grain. And, you have to consider sharpness, which may have gone down due to decreasing edge effects. PE

I plotted the curves. Wouldn't they show the effects of those 3 changes on density? Anyway, all curves were quite close (ie, nearly same contrast), so I compared their grain.

But I had not considered sharpness. The test shots of the Stouffer wedge were hand-held, so sharpness-checks must wait for the next roll.

Also, I'm a little surprised that the longer time spent in the sulfite at low pH didn't improve grain. I thought that alone would cause some improvement at low pH. It's odd, it seems that half the things I try surprise me. That tells me how little I understand the development process.

Mark

Alan Johnson
05-14-2012, 01:25 PM
I'm a little surprised that the longer time spent in the sulfite at low pH didn't improve grain. I thought that alone would cause some improvement at low pH. It's odd, it seems that half the things I try surprise me. That tells me how little I understand the development process.

Mark
Kodak Labs designing Xtol presumeably had the use of a microdensitometer that could measure RMS granularity.
I know this is not the figure they quote but their investment seems to give them an advantage over what can be done without one, for instance measure print graininess.
A difference of 6% in RMS granularity corresponds to just one "just noticeable difference" in graininess.( R.Henry,Controls in Black and White Photography p201).

albada
05-15-2012, 11:34 PM
Kodak Labs designing Xtol presumeably had the use of a microdensitometer that could measure RMS granularity.
I know this is not the figure they quote but their investment seems to give them an advantage over what can be done without one, for instance measure print graininess.
A difference of 6% in RMS granularity corresponds to just one "just noticeable difference" in graininess.( R.Henry,Controls in Black and White Photography p201).

You're making me wish I had a good 250X-1000X microscope. With that, I could simply take a digital picture of the grain and run it thru some software to score the graininess. That would be a good way of changing a subjective judgement into objective, and would probably give granularity measurements comparable to Kodak's setup.

Mark Overton

Alan Johnson
05-16-2012, 07:31 AM
How to measure small differences in granularity comes up here from time to time, sometimes it is suggested to make silver gelatin prints and report conclusions.Another method would be to make photomicrographs,I made the attached from T-max 100 using an old inexpensive microscope but have never tried this for comparing granularity.
At a guess small differences might be more visible using a more grainy film like Foma 400 but I don't recall any comment on this either.
A good method used in industry is to copy what the best Americans did which in this case would be Kodak pH 8.2.

Gerald C Koch
05-16-2012, 11:09 AM
I believe that Kodak for many years submitted prints to a group of people and had them rate the relative grainess of films in this manner. This whole topic is very subjective and even using RMS granularity is subject to criticism.

Photo Engineer
05-16-2012, 11:28 AM
We evaluated grain and sharpness both, and if color we evaluated color balance and fidelity. I was a participant in these tests from both sides. I took the test and I gave the test. Usually, we had hundreds of prints and hundreds of participants.

PE

albada
06-03-2012, 01:28 AM
Although I've been posting little, I'm still doing experiments and dialing-in the numbers on a concentrate that gives XTOL-like quality. Speaking of XTOL, the graph below is two identically exposed successive frames on the same strip, developed at the same time in XTOL. These were TMY2 for 6.5 minutes at 20C, with temperature held constant by keeping the tank in a water-bath:
52010
I expected these curves to be nearly identical. Any idea why they diverge so much? Perhaps due to differences in fluid-flow in different parts of the tank?

The shutterspeed should be consistent, as I measured it on both sides of the film-plane with my shutterspeed tester. The OM-1 consistently got 16.6 ms for 1/60th on both sides. So I doubt the differences are due to exposure. Fluid-flow is all I can think of, unless somebody has a better idea.

Anyway, the graph below shows the straighter XTOL curve from above, with my developer (in green). I'd say I need a bit more density, except the curves converge at the right. Odd.
52011

The one-litre formula for the green curve is:


Sodium sulfite ......................... 90 g
Ascorbic acid .......................... 9 g
Sodium metaborate 4 mol ...... 6.2 g
Dimezone S ............................ 0.2 g

Target pH is 8.3 (same as XTOL).
Use same times as XTOL.


Grain looks identical to XTOL in my 22x loupes. Except for the sulfite, this formula can be dissolved into 24 ml of propylene glycol, yielding a concentrate that can be used at 1+29 dilution. I'm still tweaking this formula. By the way, I found that Phenidone can be substituted at half the weight of Dimezone S, so the above formula would use 0.1 g of Phenidone.

Mark Overton

Michael R 1974
06-03-2012, 07:05 PM
Mark, for what it's worth, in comparison to the various other general purpose solvent developers I've tested, in densitometric tests I've consistently found XTOL (at stock and various dilutions) to show both the most variability roll to roll and even frame to frame, and choppier overall density growth (curve shape).

Michael

albada
06-03-2012, 09:06 PM
Mark, for what it's worth, in comparison to the various other general purpose solvent developers I've tested, in densitometric tests I've consistently found XTOL (at stock and various dilutions) to show both the most variability roll to roll and even frame to frame, and choppier overall density growth (curve shape). Michael

Michael, this makes me ask, "Then why am I trying to imitate the stuff?" Your posting also made me wonder about the choppiness of my developer, so I plotted the last few frames of the prior test-roll. I was tweaking the formula, so density varies some frame-to-frame. Here are five frames:
52035
My developer has little choppiness; certainly less than what I saw with XTOL. The linear areas are reasonably straight. I don't know why choppiness would differ, unless it's because I'm using ascorbic acid instead of ascorbate, and over 50% more borates than XTOL, and thus I probably have better buffering.

Mark Overton

Michael R 1974
06-04-2012, 07:51 AM
Hi Mark. I just thought my testing results might help explain or support the inconsistencies you've encountered with XTOL. I can't explain it though. My knowledge of photochemistry comes mostly from reading Haist, Crawley, Troop and a few others, as well as my own experience and testing. But I'm no chemist. This thread has made me want to revisit my XTOL tests though. Regarding buffering, I'm not sure how this would affect things since some of the most predictable and consistent/repeatable results I've experienced have been with both buffered and non buffered developers. XTOL has always been somewhat of an anomaly for me, and the only thing unique to it versus all the other developers I've tested is sodium isoascorbate as a developing agent. Actually it is the only developer I've ever tried with C (or variants). Not that this explains things either.