SLIMT notes for those interested

[Ulophot]

SINCE POSTING: There appears to be an anomaly here, either from errors in recording notes or running the tests. It is embarrassing, but I will need to run further tests to check the results indicated below. My sincere apologies. -- Philip

UPDATE 4/15
I'll pick up thread below, with further results and discussion.

I thought I would share a few notes from recent continuation of tests with David Kachel's SLIMT contrast-wise bleaching (http://www.davidkachel.com/assets/cont_pt3.htm) and related measures.

I’ve been using Kachel’s method of film pre-bleaching as a means of compensating development for some years. Since LF portraits by natural light, often indoors, frequently require long-ish exposures, I have been interested in seeing if I could get adequate low-value detail, shooting HP5 at 400 instead of my customary 200, in cases where large areas with such low-value detail are not crucial. (I presently use only one developer, D-23, for simplicity; hence, I have not pursued something like Microphen, which could offer a speed-gain.)
If this causes you to shake your head at one more poor fool searching after alchemic magic, I will only say, with all humility, I have been processing and printing for more than 50 years, and have done enough testing to know better.

While I have by no means exhausted the potential of SLIMT in my testing, its support of low values in compensating development for extra-long subject-luminance ranges led me recently to see if this benefit could be obtained with lower concentrations of SLIMT, so as to lessen the high-value compensating effects. My weekend’s tests used just 8 ml of SLIMT working solution in 16 oz. of water for 3 minutes, with normal agitation, prior to normal development.

I performed this test first in 35mm, shooting a controlled subject at EI 400 and then with 1 and 2 stops under- and over-exposure, for a series of 5 frames, which I repeated. Separating the two sequences onto two reels, the first got the SLIMT treatment and then was added to the other reel, and the two were then developed together normally in the same tank.

In 4x5, with another set-up and carefully defined zone values, I exposed 5 frames, ½ or ¼ second, aperture constant:
One at EI 200
Two at EI 400
One at EI 400 with a pre-exposure on Zone I using an ExpoDisc.
The 200, one of the regular 400s, and the last one received Normal development for their respective EIs, based on previous tests. The remaining 400 got SLIMT pre-bleaching as above (4ml, 3 minutes).

Results:
35mm: As shown in the attached (approx. 11x enlargement) prints, printed straight and identically, the SLIMT neg shows a marked improvement in what was about Zone II in the scene, as well as a roughly one-stop value decrease on Zone VIII. It also shows what I have noticed consistently before, which is an increased appearance of grain, for which I have no explanation (seen most clearly in the clay pot rim, if that comes across here).

I have previously compared, at EI 400, N development and N+1 with SLIMT on a outdoor scene of full range, the N+1 to restore high-value density at Zone VIII. The boost to values from II through IV by SLIMT is marked; for small format, the grain might be an issue, depending on degree of enlargement.

4x5: The EI 200, of course, shows the benefit of increased shadow detail in Zone II as well as III. However, the straight 400 negative does have the detail available; it would just be a little work to keep it when printing -- again, this for a subject in which such area(s) was confined and manageable -- and the negative tonality overall would tend to be slightly different. That was encouraging. The SLIMT neg shows about the low-value density of the 200 neg. Grain is not an issue in this format at the sizes I print (up to 11x14 with some cropping); the SLIMT treatment, however, does affect the total range differently from exposure changes, so there is a trade-off to be considered with certain subjects. For a subject with important luminances going into Zones IX or X , this slight compensating effect, combined with the low-value support, could be just the thing to allow the EI 400, allowing, for instance, a 2-second rather than 4-second (requiring 5 seconds when compensated) exposure.

The ExpoDisc neg shows only slight improvement and the extra hint of overall fog it necessarily entails. I won’t be pursuing this avenue further. (Others have shown why Adams's use in Poloroid prints differs from standard negative photography.) SLIMT is a better tool for me.

Trade-off is the key word here. We all want ideal negatives to make ideal prints. In my work, however, this more gentle use of SLIMT than I had considered previously, adds one more tool to the box.

[Peter De Smidt]

Thanks for sharing!

[Alan9940]

Thanks for sharing these notes on your research with SLIMT and film. I have been playing around with it on contact printing papers--mostly Adox Lupex--for about 6 months and I, too, have found that much lower concentrations of the working solution are needed to obtain the effect I'm looking for. To be clear on my methods, I mix a permanent stock, then dilute that into a working stock A which is further diluted to make a working solution. At first, I tried 10ml A to 1L water for 3 mins, but that concentration reduced the contrast more than I needed/wanted. Lately, I've been using 1-3ml per liter water for 1-3 mins and that seems to get me where I want; a slight reduction in contrast.

[Ulophot]

(If you're just tuning in here, please read my original post in this thread to make sense of this one.)

Here's the synopsis:
I'm finding anomalous behavior between different formats of HP5. My 35mm result as posted was on target; the SLIMT result for the 4x5 was not.

Here's the plot thickens part:
I am extremely relieved to report that I am not, as I was beginning to fear, "losing it" entirely or simply incompetent in photographic technique. I had not reviewed the 4x5 negatives with adequate care before my original post, above. After printing the Normal and SLIMT ones and seeing no discernible difference, I reviewed them all again. What I had reported was true except for the 4x5 SLIMT neg.

I repeated the 4x5 test again, with just two sheets, exposed identically at EI 400, and with the same procedure: the first went into the tank for 3 min of SLIMT, which was then poured out, the second sheet added, and normal development for 400 given. Again the negatives were virtually identical, with the SLIMT only flattening the high values but having no effect on boosting the low ones. Thus, my embarrassed note.

That made me think that I must have allowed some error in the 35mm test, despite every caution. Today, I repeated the 35mm test, again scrupulously checking for illumination changes as I went along. I exposed 15 frames identically this time, and developed as I had the 4x5, with half the roll getting SLIMT before being added to the other half and developed together normally. When the negatives dried, I could see extra density in the SLIMT negs' low values (Zones II and III), and the prints bore this out, just as in the previous 35mm test. That was encouraging, but perplexing.

Putting on my investigator's hat here, I see few potential variables:
Unlikely:
1. The HP5 emulsion is different for the 4x5 film
2. Some other layer of the film composite (adhesive layer?) is reacting with the SLIMT or something

Perhaps more likely?
3. I develop the 35mm in a nickel-plated Kindermann SS tank; the 4x5 goes in my plastic SP-445. The metal makes a difference.

I have not yet tested 120 HP5 for this, which also goes in a Kindermann tank. That will be next.
Otherwise, I will see if the process's inventor, David Kachel, has any insights, and welcome anyone who who knows enough chemistry to offer a hypothesis.

I'll add new posts to this thread as I go along.

[Mark Sampson]

There's no guarantee that 35mm and sheet film versions of a film with the same name have identical emulsions. You might ask Ilford about that.
For example;1) the emulsions are on a different base. 2) the backing on 35mm(to prevent scratching) will be different than on the sheet film. 3) anti-halation coatings may or may not differ. 4) the emulsion itself my be subtly different for reasons known only to the manufacturer. When I worked for Kodak, once or twice I worked on new film projects with a film designer. Not exactly relevant here, but I did come away with a glimpse of the enormous complexity of film design and manufacture.
I wish you the best of luck solving this issue- but you're exploring way off the map here, and anomalous results should be no surprise. Don't be discouraged when I point out that Kodak (and no doubt other manufactures)repeated tests many times to ensure consistent results before releasing a film or publishing data.

[esearing]

Just thinkin' with no practical experience....

The image size of a 135 film is much smaller than on a 4x5 sheet. I would expect the grains to be of similar size but the larger sheet would have smoother contrast as the image transitions from light to dark. You may have to use a busy image to see the effect or have areas with extreme contrast on sheet film. Also LF shutter variances between one shot and the next may vary as much as 1/4 stop, plus any change of light.

[Ulophot]

Thanks, gents.

I'll check around regarding emulsion differences; I would not expect Ilford to respond on that matter, but I can try.

A 1/4-stop would not account for my results in this case, and I was careful to measure light at the moment of exposure, and the result was identical in both cases. I did consider the total film area. It was similar in the 35mm and 4x5 experiments relative to volume of solutions.

[Ulophot]

I overlooked one aspect in my first post, which is that my SLIMT dilution is even greater than indicated. Kachel's working stock would be 50ml each of ferricyanide and bromide in a liter, or 25ml each in a half-liter (roughly 16 oz). I have been making a work stock from only 5ml each of ferricyanide and bromide -- 1/5 the strength -- from which I make the working solution with 8ml in 16 oz of water.

Have written to Ilford. David Kachel kindly replied but had no new insight on this particular anomaly, though he echoed Mark's note, above, that an emulsion difference is by no means to be discounted.
Stay tuned...

[ic-racer]

It is kind of difficult to see the effect on my computer monitor, do you have the H&D curves for those two?

[Doremus Scudder]

Philip,

I've been following this thread with interest, since I use SLIMTs a lot for contrast reduction. A couple of things jump out at me:

First, as I understand the SLIMT process, the ferricyanide/bromide solution bleaches out some of the latent image, i.e., either renders it "unexposed," or dissolves it away. In either case, those molecules affected, though exposed earlier, now will not develop out. I can find no logical reason with this mechanism, that low values in the treated negatives should be strengthened directly by the SLIMT process itself.

Any comparative difference in the low values of SLIMT negatives compared to those developed N-X to achieve the same highlight density would have simply be caused by the speed loss due to reduced development and the resulting underexposure of those shadows in comparison to the fully-developed shadows on the negatives treated with SLIMT.

Hence, there should be no difference in shadow values in negatives exposed identically and developed identically regardless of whether or not they have been treated with SLIMT bleaching. The fact that you report this leads me to believe that something else is amiss with your testing. Either that, or there is some mysterious way that a ferricyanide/bromide bleach can add extra film speed, which I find highly unlikely.

Next, the real comparison to test for, IM-HO, would be to compare curves between a negative exposed and developed N-X (i.e., given the slightly more exposure needed for N- development and then developed for less time than normal to obtain a traditional N-X contraction) and one exposed at the normal E.I. and then given a SLIMT treatment and subsequently developed at the normal development time to arrive at the same N-X contraction as the control negative with reduced development.

Additionally, the fact that you find your 4x5 negative tests to yield almost identical negatives simply indicates to me that your SLIMT bleach was too weak to make any substantial difference. You may indeed be uncovering a difference between the 35mm and sheet-film versions of this film. Other factors, such as anti-halation dyes, couplers, hardening, etc. may also have an effect on the way the SLIMT reacts with the emulsion.

I look forward to hearing your thoughts on the above.

Best,

Doremus