Dark band down center of negatives

Please see the attached screenshot of the preview scan from the scanner.

I'm seeing a dark band down the center of the negative, running the length of the film. Not sure where I should start looking to eliminate the problem. Light leak somewhere? Chemical problem? This is not the first roll I've seen this, but it's not consistent, and has happened with 2 entirely different cameras. I'm doing something wrong somewhere.

Hasselblad 500C/M, HP5+ in D76 1:1 for 12 minutes. Reasonably fresh chemicals.

Thanks for any suggestions.

Light leaks leave light bands, not dark ones on a positive print. I'd go with an agitation issue and slight under development of the center of the film.

Are the bands there when you look at the negatives on a light table? Sometimes, the film doesn't lay flat in the scanner and shows bands like this. But when I look at the negative the bands aren't there.

Agitation, definitely. Too much flipping, not enough spinning, or too much spinning, not enough flipping (that would be my first choice, but does anyone use tanks with agitator rods anymore?) perhaps combined with not enough, total.

I was actually somewhat distracted by a phone call while processing that roll, so my agitation could've been off. Will try another roll, being more mindful of the agitation.

The negatives are quite flat in the scanner, since I scan them "bend upwards" with Betterscanning glass holders. It's difficult to see the band with just a loupe, but it does seem barely visible. It becomes worse as I dial up the contrast in post. I may also try some wet prints to see how those look.

Thanks

I agree this is lack of agitation in the first 15 seconds of development.. You must twist invert twist invert very aggressively to get rid of this ... get developer in quick and then agitate.

Bob-D659 said:

Light leaks leave light bands, not dark ones on a positive print. I'd go with an agitation issue and slight under development of the center of the film.

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jackbaty said:

I'm seeing a dark band down the center of the negative, running the length of the film.

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Your posted images don't show this. The negatives posted have a center that is is less dense. Less silver developed on the negative. More clear or lighter in the center. Are you sure that is what you are seeing. Are you looking at the negatives on a light box or looking at them with a dark background? When you look at thin negatives against a dark background you can see a misleading positive image.

Negatives that are lighter in the middle are frequently the result of exhaustion of the developer during development, leading to less development near the center of the negative. What is your processing volume per 8x10" of film?

Another vote for agitation issues, although I might say the "darker" center could be ok, but the lighter edges (which are inconsistent here) suffer from surge, or over-development from having more agitation at the edges, from inverting the tank, etc. I find this problem more difficult to eliminate with 120 film than either sheet film (which I do in trays, manual shuffling, constant agitation), or 35mm. You have to agitate enough to get the same exchange of chems in the center as you get at the edges. If the agitation is too "violent", you can have surge also. I find it more evident with some developers than others.
My current successes have come from a 1 1/2 minute initial agitation, then 15 sec agitation every 1 1/2 minutes. My thinking was since the surge occurs during agitation, I do it less often, but do it longer, to ensure good exchange in the center of the film. My technique is an inverted swirl (like most folks do with reel tanks), but a slow consistent one for 15 sec.
This is counter to most advice I have read over the years, but it works for me with Ilford films and HC-110 1:60.

You are using stainless steel reels and tanks? Then the answer is simple--you are overfilling your tanks and the edges of the reels moving through the developer is causing uneven development as there is no developer agitation at the center of the film. Leave an air space in your tank.

ic-racer said:

Your posted images don't show this. Are you sure that is what you are seeing. Are you looking at the negatives on a light box or looking at them with a dark background? When you look at thin negatives against a dark background you can see a misleading positive image.

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That's odd, I can see the shading on my monitor.

Bob-D659 said:

That's odd, I can see the shading on my monitor.

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The negatives posted are light in the center, not dark. He is not posting a contact print, (but I may be wrong as it is not clearly stated).

Hikari said:

You are using stainless steel reels and tanks? Then the answer is simple--you are overfilling your tanks and the edges of the reels moving through the developer is causing uneven development as there is no developer agitation at the center of the film. Leave an air space in your tank.

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Yep, exactly. One thing to add which gave the final 'evennness' for me is to do an aggressive inversion motion, but be certain to pause for a bit after each flip (meaning both the first flip and the 'return' flip). This seemed to give the developer the time it needed to actually flow and refresh across the whole of the roll.

ic-racer said:

The negatives posted are light in the center, not dark. He is not posting a contact print, (but I may be wrong as it is not clearly stated).

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Could be contacts prints or inverted scans of negatives, the results should appear the same. I agree, but I'm so used to people mixing up terms, I just reply to a posted image that I see, and don't worry too much if the terminology is wrong, sometimes.

+1 for Hikari's suggestion, I forgot to mention that. I measured the amount of water to just fill the tank to the top of the reel, then add an ounce or two for safety. For my tank (Kinderman tank, Hewes reel) I use exactly 425cc. Covers the reel with plenty of room for chems to move around.