HC-110 Dil H, 2 rolls - question

I usually only develop one roll at a time, but today I have two rolls I want to do. My 'formula' for this film (Kodak SO-370, an oddball film), has been Dil H for 12:30 in a Paterson tank. For one roll, I had been using 400ml to get to the recommended/required 6ml HC-110 per roll, and things have been great. But I just realized that the Paterson tank doesn't hold 800ml (or at least I don't think it does) which I would need to get to 12ml.

So my options are to only do one roll at a time, or change dilution. I think I'd rather change dilution, but I'm not 100% sure how to adjust my developing time. Is HC-110 a straight reciprocal? ie., double the dilution (H to B) equals half the time? How does the increase in dilution and decrease in time affect the end negative (not just with HC-110, but in general)?

There is no general purpose answer to your questions.

The usual rule of thumb for HC110 is that dilution B times are standard, and dilution H times are approximately twice the dilution B times, but different films will respond in slightly different ways.

The film you are shooting is very old, so base fog concerns will skew normal calculations. It is also one where there are few people out there with extensive experience with it, who might be able to advise.

A traffic surveillance film like the one you are using will have originally been optimized for different criteria than general purpose films, so there is no easy way to predict how it will respond to changes in dilution and time.

HC110 was formulated originally to give similar results at different dilutions. Other developers were not necessarily designed with the same priorities in mind.

If I were you I would either:

1) develop one roll at a time; or
2) get another, larger tank for the times when you want to develop two rolls; or
3) do extensive testing to determine appropriate times for different dilutions.

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Throw out the rule of 6ml minimum of HC-110 per roll of film.

I use HC-110 diluted 1:100. That translates to 3ml per roll of 135 film. No problems!

Thanks Matt.

As for the film, it seems I have become the 'expert' in it, as there is absolutely no info available for it other than what I have posted here (in another thread), and one other guy that had 1 roll of it. I've run about 6 rolls of it so far, and it has been pretty decent, and the price for it couldn't be beat (3 sealed bricks of 12 rolls and a butt-load of other stuff for <$40). I rated it at 64 ASA based on some tests, and the 12:30 dev time (at 74°F) was also through some tests, and that seemed to be the best for it.

Covington does say that HC-110 is a reciprocal developer, but I just wanted to make sure. So as soon as my water gets to 68° F, I'm going to do a dilution B for 8 minutes, and see how that goes. Nothing on either roll is very important, as they were tests of a 'new' lens, but I expect they'll be fine.

Negatives are drying now. At first glance they look good.

While you can, in fact, get by with less than 6ml per roll, and get great results, you may not get consistent negatives that give you 100% repeatable results.
I've used HC-110 at 1+50 and 1+100 at the volume the tank holds. At these two dilutions obviously the amount of concentrate varies, and so did the results where the 1+100 had a bit more compensating effect, possibly due to exhaustion of developer in the highlights.

I say: Pick one amount of developer per roll and be consistent with it, and you will be fine irrespective of what that value is, as long as you don't deviate from what you choose and you don't pick something ridiculously low.