The following post is embarrassing to me, but I’ll survive, especially if a solution if found.
With a little vacation time recently, I finally got around to testing specifically for even agitation with the SP-445 tank, which I have been using for about two years. I had decided to test, even though I have been generally happy with image results from the start, only occasionally noticing a slight variation in large even-toned areas that left me wondering if something were a little amiss. I’m not a landscape-and-sky photographer, mostly; portraits or other more complex subjects that tend to hide such variations are my line. Someone will ask, then, why bother? Because it’s a simple, very basic matter and I don’t like settling for “okay,” least of all in matters of basic craft.
With larger film batches I use a Jobo tank on a roller for continuous agitation and get very even tone indeed. The 445’s low sheet capacity, however, is a great addition. I am not going to return to tray processing. Others report nice even results from the 445; it’s a valuable piece of equipment.
I have been using the proper broadside end-over-end agitation, although 4 inversions over 10 seconds every minute rather than every 30 sec., and in a slightly more continuous, rotisserie sort of motion than the faster “flip” approach demonstrated in the Stearman Press video. But I also tried that variation, and have tried agitating every 30 seconds. My results have been a bit disappointing in all cases, with a noticeable mottling. It’s worse with a very smooth, continuous inversion, and also with a pronounced “drop” or “push” at the mid- and end-point of each inversion cycle (i.e., over and back upright), rather than revolving strictly around an imaginary axis. A slight drop, my standard for decades with SS tanks and roll film, gave me the example shown.
My developer is D-23 1:1, nothing unusual; Normal development is 9 minutes at 68 F. I have questioned whether my two-plus-year-old Metol might be at fault, but that makes no immediate sense; overall densities have not diminished relative to exposure/development. It’s stored in brown glass out of direct sunlight, though the temp is often in the 80s in the summer. Anyway, the mottling varies from run to run and appears to be an agitation issue.
My test targets have been, variously, a large sheet of matte white card stock taped to my flat outside house wall under overcast conditions; two sheets of letter-sized copier paper taped next to each other on a flat surface and illuminated with bounced light; an area of rich blue sky. No variation across the field in any direction read by my spot meter in any of these cases.
I have tested with one sheet or two in the tank, both with emulsion toward the tank center, i.e., film loaded on inner side of holder(s) when holder(s) inserted; and with emulsion toward the outer tank walls from the outer sides.
The image shown, scanned from a contact print, approx. Grade 2 ½, is the best result I have managed to achieve after a half-dozen tests, still showing the mottling. The dark center line is a small space between two sheets of paper on my upright piano board, photographed out of focus.
The last time I recall having to struggle to get even agitation was back in the days of 35mm Tech Pan and Technidol (some of you surely remember that joy), which required a very quick ¾-inversion flip of the tank with no rotation a couple of times every 30 seconds.
Any ideas?
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