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.

202612202611

[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

[Ulophot]

Hi, icracer. I do not have the ability to analyze and create curves. I am reporting on both visual examination of the negs on a lightbox, and on prints made identically from representative negs. See more below. i realize that this may seem to leave lots of wiggle room for error to someone used to that level of precision. If I should be proven wrong about this anomaly, so be it; I have no ego investment in this; I'm just following a surprising effect and trying to understand its cause for practical field use.

Hi, Doremus, and thanks as always for your thoughtful and experienced insights.

I am beginning the suspect the same with regard to an emulsion and/or other-layer difference between the formats. I will process a 120 roll (all frames of a controlled subject, identically exposed at EI 400; half the roll processed with the SLIMT and then added to the other half, the two developed together in the same tank with N development. We'll see what happens.

As I have indicated, the low-value boost came as quite a surprise, and if I had not been able to replicate it, with care against variables at each step, I would naturally have dismissed it. I assumed I had made an error with the 35mm after seeing no effect in the 4x5; I tested both again and got the same results as before. I have no idea why this approximately 1/2-stop or so density increase is occurring at the low-end-- as you say, it appears to make no sense, since the higher values are being slightly depressed. It would be interesting for someone else to perform the same test. (And haven't we heard enough claims over the decades about miraculous speed increases?)
As you know, Kachel notes that negative films tend to require the KBr solution to prevent fog, which I am using. I don't see fog, looking at the film or printing, though this is something I can trying printing for, i.e., making prints that place clear film around Zone V or VI to compare them.


I'm not sure how this will all pan out. I can only tell you that I am seeing the same result repeatedly in 35, which I first ascribed to N+1 with SLIMT compared with N without, shooting the same sort of test. And, there is an apparent grain increase evident in the small format enlargements, as usual with SLIMT treatment.

[Ulophot]

4/18

I have now tested 120 size, and have gotten results similar to those in 35mm, i.e., a boost of roughly ½ stop in the Zone II-III range and a slight decrease of density in the high values. The decrease in the high values appears slightly less to me than in my 35mm tests, but I don’t have identical values to compare. What I noticed in this test, however, was what appeared to be a slight boost up into the upper mid-values as well. However, closer examination showed that in those areas, e.g, out-of-focus background objects through an aluminum-screened window, and the slightly fuzzy surface of a darkish T-shirt, had a “texture” in which tiny “points” of very low value were getting the boost from the SLIMT, thus averaging out the value slightly higher, much as a fine checkerboard pattern of black and white, if seen from a distance sufficient that the eye’s resolving power is challenged, appears solid gray. This middle-value difference is small and perhaps a little more noticeable in the 120 size because of the smoother tonality and less obvious grain; it appears mostly as a decrease in texture, as in the T-shirt surface.

After making prints of two randomly selected frames, one from each half of the roll (see procedure in my original and subsequent post), I chose two other frames, just in case they might show some difference I was not seeing in reviewing the negatives. While this is not a scientifically rigorous application of method, results did remain consistent. I had shot the test under heavy overcast and continued checking light readings throughout the test, as before.

I tested to see if the density increase might be due to overall fogging, which is the only other thing I could think of that would be logical with respect to the way SLIMTs work. My hypothesis then would be that, although I maintain Kachel’s ferricyanide-bromide ratio, the extreme dilution I used for these tests crosses some threshold for the bromide which reduces its anti-fogging capacity. I printed the clear film between frames (relatively wide in my 645 film) and adjacent in-frame toe values, approx. Zones 0-I ½, to values between a high V and low VI, i.e., on the straight-line portion of the paper curve, where any difference would show up best. The normal and SLIMT prints, developed together, are indistinguishable.

So, the mystery remains, for me, as to why this is happening at all. I could add, that my “Grade 2” is a bit higher-contrast than normal; I print with a cold light source and Ilford filters, but without a CC40Y, so my 2 is more like 2 ½, which may mean that the half-stop difference I am getting in the low values would be slightly less in someone else’s prints. However, not much, and it is there and is repeatable in 35mm and 120. It seems increasingly that either the emulsion or other layers in the sheet film versions of HP5 somehow respond differently. However I wish the roles were reversed! Whether I can coax the same behavior from 4x5—which, is, recall, why I started this whole process to begin with—using a different SLIMT concentration, will be my next test. Frankly, I’ll be astonished if it works, but having come this far, I may as well give it a try.

[Ulophot]

I am adding to this thread again in order to, potentially, close it out; others may have comments to add.

Thanks to the suggestions in private of one of our more experienced and always thoughtful members, I have discovered that a variable I had not considered, rather than the SLIMT bleach, has been causing the density increase, and I worry about even mentioning it, lest I trigger one more debate about it’s use. However, in order to clear the air about my attributions of unexplained density increase to SLIMT, I feel properly obliged to do so. Pre-soaking the Normal, non-SLIMT-treated negative in water evens its density with the SLIMT one, other than a slightly denser top end; even my very dilute SLIMT had some effect there. That is, with this film, in my case, pre-soaking apparently just gives the developer a little more time to work.

I will leave my thoughts off here for the reason given above, noting only that I now remember seeing Phil Davis’s report of increased contrast due to presoaking, which he investigated rather thoroughly with various films and varying results years ago.
Thanks to all of you who contributed to my little side trip through the seeming anomaly. The main thing is to keep learning!