I have not solved photography and don't know the answer to your question; however your problem interested me enough to watch a tutorial video about the SP-445 tank, so I have some idea of how the tank is constructed and how it is supposed to work, and on the basis of that very limited bit of information, I offer the following for your consideration. First of all, it is clear that this aberration is caused by uneven development, i.e., namely that the edge received less development than other parts of the negative and therefore the positive is darker in the affected areas. Second, and very importantly,
the problem is not limited to the right side of the image. If you look very carefully at your scan you will see that the problem occurs on the left side as well. It is not so obvious along the full length of the image, but it is apparent in the lower left corner of the positive (the difference can be made more obvious by running the image through different filters in PhotoShop and, I assume, other comparable programs). So taken together, what does all of this suggest? My guess, and here I cannot overemphasize the word "guess," is that you may have inadvertently loaded the negative in the an orientation opposite to that recommended by the maker, i.e., the film was loaded with the emulsion side facing the continuous, unbroken, flat part of the holder vs. having the emulsion side facing outward toward the intermittently-spaced tabs that hold the sheet film in place to prevent it floating away from the holder. If that is indeed what happened, then it may be possible that the developer did not reach those edges of the film as quickly as the developer covered the remainder of the negative, e.g., because the film edges may have adhered slightly to the flat parts of the holder, partially on the positive left, and more completely on the positive right, for a brief time - certainly longer than 1 or 2 seconds - and the agitation provided was not sufficient to dislodge the stuck parts quickly enough to give even development across the entire negative. I do not know the proper name for this adhesion but what I am thinking of is not unlike what happens when a bit of liquid or humidity causes a dry negative to stick to another negative, to a polyethylene sleeve, or to some other material. I assume the problem could be exacerbated if you happened to use only one holder and cross loaded it so that there was more pressure on the edges than would otherwise occur, but I am certainly not suggesting that was the case. I do not assert that this theory is correct, and will not be the least bit embarrassed or ashamed if it is determined to be wrong. In the meantime, I too recommend that you pre-soak to minimize this problem going forward if you are not already using a pre-soak, and I also recommend that you contact the manufacturer of the SP-445 directly to see what they might have to say about the cause and cure, especially if the problem is a recurrent one.
N. Riley
http://normarileyphotography.com
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