Underdevelopment of top roll in 2-reel tank?

Hi all,

I just got a Paterson 3 tank (does 2 rolls of 120 film at a time), and developed my first two rolls in it. Pan-F+ film with Xtol 1+1, with a development time of about 7m 15s. I load film onto the reels in a changing bag, and develop in the light, pouring the chemicals in through the top of the tank (as opposed to lowering the reels into an already filled tank in a darkroom).

The roll that was on top seems to be a bit less developed than the roll that was on the bottom, and I'm wondering if the modest difference in time exposed to developer between the two rolls could be the issue -- i.e. the bottom of the tank fills first and empties last in my process. I would guess the time difference amounts to about 20 seconds more time in the developer for the bottom roll out of a total of 435 seconds total development time. So maybe 5% of the development time. Any thoughts on whether that could cause a detectable difference in negative density? (I'm quite sure I had enough solution, and the upper roll is evenly developed and looks fine, except that it's slightly, but detectably, less dense than the bottom roll.)

My first instinct is to aim for longer development times -- maybe 10 minutes or more -- so that the 20-second time difference represents a smaller percentage of the total development time. Other suggestions or thoughts are welcome.

villagephotog said:

Hi all,

My first instinct is to aim for longer development times -- maybe 10 minutes or more -- so that the 20-second time difference represents a smaller percentage of the total development time. Other suggestions or thoughts are welcome.

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That's probably a good idea in general. I'm not sure how short your development time is, but anything less than 7.5 minutes introduces the likelihood of timing problems. I use the smaller tank that does two 35mm or one 120 roll and never seen this, but I can imagine this might be an issue with taller tanks.

Actually, if you are inverting the tank to empty it, the bottom of the tank fills first and empties first, so it works out to be basically even.
In any event, a developing time over five minutes should average things out nicely; things should be fine with times over three minutes, assuming regular agitation.
How and how frequently are you agitating?

villagephotog said:

I'm wondering if the modest difference in time exposed to developer between the two rolls could be the issue

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Probably not, really. The time difference is rather small for very apparent differences in the negatives. The first thing to verify is that there really is difference in development, and that in itself will likely be quite challenging. Contact printing both rolls may give some insight, as well as reflecting on how you exposed both rolls (as the differences may just as well be due to exposure for all we know now).

koraks said:

the differences may just as well be due to exposure for all we know

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Or even due to differences in the films.
As Pan F is famous for losing density if you delay developing your exposed film, is there a chance that the top roll was exposed a significant time before development?

MattKing said:

Actually, if you are inverting the tank to empty it, the bottom of the tank fills first and empties first, so it works out to be basically even.

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Ah, of course that's right; I wasn't thinking it all the way through. I think that eliminates the possibility that it was a difference in time immersed in developer. I did say "seems"; I wasn't sure. It was just one possibility I was considering.

As regards other suggestions made (re: exposure, age of film etc.) I wouldn't even have suspected the tank in the first place except that all other parameters are essentially identical. It was a lens test, so it was the same subject, shot under consistent light (at least within the range of detectability), same range of aperture/shutter speed combinations, both rolls bought 3 days ago from B&H, shot within a span of 15 minutes and developed 2 hours later. The only difference was the lens. So maybe one of the lenses has a little imprecision in its aperture setting; that would be my next guess. Shutter speeds on both are pretty accurate, but that might also be a bit of a wildcard.

Anyway, thanks all. I think you've helped me understand that I don't need to worry about this particular issue when using that tank.

What camera and lenses?
And are there any filters in the mix?
If we are talking about leaf shutters, then one of the shutters might very well be opening and closing at a different rate than the other, even if the total time that the shutters are open works out to be the same.
And of course, f/stops and T/stops are rarely the same, although the difference is frequently small.

If both rolls of film were really identical (same production batch and storage conditions) which seems to be the case, check the frame numbers and edge markings to see if they differ in density.

Can you define "seems". I think you mean that you think but aren't 100% sure that all the negs on the top roll look less developed than the bottom. If it is a perception but one that you are unsure then try printing two identical negs, one from each film at the same exposure and grade and see if there is a noticeable difference in the prints.

If you are hybrid and scan only then I have no idea how you set up two prints identically but presumably a few here do. If such a test is possible with a scanner then try it

Then let us know what you find. A digital picture of two negs might help us say if there is a difference in the negatives

pentaxuser

This provides an excellent argument for testing both lenses on the same roll of film!

Well, I think you guys very adequately answered my question about the developing tank. Thanks again for that! But taking the further questions in order:

MattKing said:

What camera and lenses?
And are there any filters in the mix?

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A Mamiya Universal and two Mamiya Press lenses: a 50mm f/6.3 and a 65mm f/6.3
No filters. I wasn't trying to compare them to each other—rather I was looking for possible optical problems in each one separately (the 50 was recently adjusted and I just bought the 65). But even so, I ended up using exactly the same set up for both.

koraks said:

If both rolls of film were really identical (same production batch and storage conditions) which seems to be the case, check the frame numbers and edge markings to see if they differ in density.

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I haven't had time to do that yet (had to work today; I hate when that happens), but it's a good idea. However, the density difference is pretty small, and I'm not sure I'll be able to see it conclusively in the edge markings. But I'll check, even though, at this point, it's only of academic interest to me.

pentaxuser said:

Can you define "seems". I think you mean that you think but aren't 100% sure that all the negs on the top roll look less developed than the bottom.

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By "seems" I meant that I wasn't sure if underdevelopment was really the cause. The images on that roll definitely are slightly less dense, at least the 4 or 5 that I compared this morning. I'll look closer tonight and maybe I'll find a frame that strongly indicates it was actually exposure after all (as I now think is most likely).

MattKing said:

This provides an excellent argument for testing both lenses on the same roll of film!

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Yes, it would eliminate this question, for sure!

As I said, I was testing for optical performance, and individually, not against each other. My best guess is that one of the lenses doesn't actually achieve the exact aperture it's marked for and that the error is consistent (i.e. 1/3rd of a stop too narrow for the whole range of aperture settings, or something like that). The 65mm is a very old design with an old-style Seikosha-S shutter with a non-clicked aperture setting lever that has some degree of play in it. But if it's a third of a stop off, that's no big deal to me.

villagephotog said:

A Mamiya Universal and two Mamiya Press lenses: a 50mm f/6.3 and a 65mm f/6.3

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Hope you are comparing the centre of the frame - a 50mm on a Mamiya Universal is bound to show at least a bit of cosine error darkening near the edges!

MattKing said:

Hope you are comparing the centre of the frame - a 50mm on a Mamiya Universal is bound to show at least a bit of cosine error darkening near the edges!

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Yes, that's a good thought, but I was indeed judging the center portion of the frame.

Of more concern to me is that I don't think the repair of that lens was particularly successful. It was quite significantly soft on one side, and from my quick look this morning I don't think the repair shop improved it all that much. Some, but not as much as I was hoping for. I'll have to look closer tonight to really know. The vagaries of using 50-year-old gear!

On the upside, my new-to-me 65mm lens, on admittedly first glance, looks pretty good—didn't see any obvious problems. It hasn't been used much, which is clear from its condition. It came with its original box, albeit now very tattered. Fun to have a box—and original styrofoam!—from circa 1965. Of course, the styrofoam will still be around 500 years from now.

when you say under development, do you mean the entire roll looks thinner, or part of the roll ? My first thought is that there wasn't enough chemistry in the tank and the top roll wasn't covered fully = less development. are the edge markings same as the bottom roll ? if you can post a photo of the roll in question, that might help.

I have a tank that takes 4 rolls of 120. I fill and empty through the lid. I've never noticed a difference in development of the top and bottom rolls, but admit I've never looked for such variation. I don't own a densitometer, for what that's worth. My dev times tend to be more in the 11 minute range.

So I think there isn't a huge difference. A subtle one? Haven't noticed, but can't rule it out either.