How to determine the correct amount of developer concentrate per roll for inversion and rotary processing

I've been doing some developing of 35mm black and white film using Ilford's DD-X developer with a Jobo 1520 tank and inversion agitation. Up to this point I've not been very economical with the chemistry and have been using 100ml of developer to 400ml of water to achieve the 1+4 dilution recommended by Ilford to develop a single roll of film in the 1520 (which has an ~500ml capacity).

I'm trying to understand what is the minimum amount of DD-X necessary to develop a roll of film using both inversion and rotary processing.

Ilford's data sheet for DD-X says this:

AVAILABILITY AND CAPACITY
ILFOTEC DD-X is available in 1 litre bottles world-wide.
Used at 1+4 for one shot processing it will develop 16x 135/36 films.
If reuse techniques are used, it will develop up to 50x 135/36 or 120 films

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According to my interpretation of this, for one-shot processing, I require 62.5ml of DD-X in the working solution in order to develop a single roll of 35mm film. I get that simply from

1000ml/16 = 62.5 ml per roll.

Given that, using 100ml of developer in the 1520 seems to be more than enough to avoid developer exhaustion for a single roll of 35mm film. But if I'm interpreting Ilford's instructions correctly, then I can't develop two rolls of film in the 1520 using DD-X one-shot because that would require (1) * 62.5 + (4) * 62.5 ml = 312.5 ml per roll or 625 ml for two rolls. which exceeds the capacity of the 1520. Am I understanding this correctly?

I'd also like to give rotary processing a try and I'm not at all sure how much developer is required for that. Here's what the Ilford data sheet says about rotary processing using DD-X:

Rotary tube processors have very similar processing conditions to spiral tank processing by hand, except they process with small amounts of solution using continuous agitation and can be pre-programmed. ILFOTEC DD-X developer can be used to process films in rotary processors using recommended dilutions at 20°C (68°F).

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I'm not entirely sure what this means in terms of the amount of developer required. Does each roll of film still require 62.5ml of developer in the working solution for rotary processing? Or does it require a different amount?

I'm a bit confused about rotary processing in general because it's not clear to me how the portions of the developer not immediately beneath the reel in the tube are able to act on it i.e. how much of the, say, 62.5ml of developer in the concentrate actually ever comes into contact with the film during rotary processing? Does the rotary process somehow ensure that all of the developer solution is able to come into contact with the film during the development process in order to avoid local exhaustion of the developer? Maybe a dumb question, but I'm not able to exactly visualize the movement of the developer solution in the tube during rotary processing.

This simplifies things quite a bit, but with rotary agitation, think of the developer staying in place and the film moving through it.
With everything turned on its side, you need enough solution in the tube to be able to cover nearly half of the reel with fluid.
You still need 62.5 ml of concentrate per roll with rotary development.

MattKing said:

This simplifies things quite a bit, but with rotary agitation, think of the developer staying in place and the film moving through it.
With everything turned on its side, you need enough solution in the tube to be able to cover nearly half of the reel with fluid.
You still need 62.5 ml of concentrate per roll with rotary development.

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That's exactly the way I was visualizing it But the lead to my confusion, since if the developer stayed in place then very little of it would ever come into contact with the moving film reel during the development time. So I'm assuming there is also lateral movement of the fluid along the long dimension of the tube as the rotating reel displaces it.

In addition to moving because of turbulence, the developer also constantly gets dragged up the moving film and then drains down.

MattKing said:

In addition to moving because of turbulence, the developer also constantly gets dragged up the moving film and then drains down.

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That makes sense, thanks Matt.

I cant speak to Jobo, I have a Unicolor film and drum and motor base. With a SS tank I need 10oz of chemistry for one roll of 35mm. The Unicolor tanks needs 8oz, reason is that the chemistry only needs to cover 1/2 the reel when on it's side being rotated though chemistry. The real saving comes when adding additional rolls, 2 rolls only takes 12OZ, 4 rolls 24OZ, 48oz or 8 rolls the max for a Unicolor tank. I've used DDX, D76, Edwal FG, Clayton F76 and F90 without issues in terms of developer capacity.

In my earlier days when I used DDX I simply divided the capacity of the tank, say 250 ml, if it was a Jobo 1500 35mm tank by 5 (1+4) so 50ml of DDX. All my negatives looked fine. So what did I do if it was a 120 film which is the same surface area as a 35mm film but requires say 480ml of liquid? I suspect I then simply divided the 480 by 5 as well so that was 46ml more of DDX than for a 135 film and, yes. this exceeds your 62.5ml by quite a lot so was I wasting 46 ml of concentrate in my case or 33.5ml by your calculation?

The thing about 62.5ml is that if this is the minimum required then why does Ilford give the following table on page 2:

Tank Size (ml) Dilution 1+4 Concentrate / Water 100 20/80 150 30/120 200 40/160 250 50/200 300 60/240 350 70/280 400 80/320 450 90/360 500 100/400 600 120/480 700 140/560 800 160/640 900 180/720 1000 200/800 2000 400/1600

I have highlighted the Ilford amounts on bold for both a 35mm tank and a 120 tank and lford seem to suggest that on a simple ratio of 1+4 basis the amount of concentrate has to rise. How do we reconcile this with a minimum quantity of concentrate for a 135 and 120 film being the same ?

Well the only way I can think of is that some but not all 120 tanks will accept 2x120 films in the same overall quantity of fluid. This being true of a Jobo 120 tank. Thus the minimum is 50ml of concentrate for 1 x 120 and 100 ml of concentrate for 2 x 120

So my logic and seemingly backed up by Ilford's figures suggest that 50ml minimum of concentrate is right for 135 tanks and 120 tanks (Jobo) thus saving you 12.5 ml of concentrate per film. This may seem a small saving but it adds up over say 10 films given the price of DDX

So what of the other amounts in the Ilford table? Frankly. I just don't know. They are of course right mathematically but are they nonsensical from the minimum concentrate requirement aspect? I suspect they may be and as they are only two sizes of roll film anyway do the other quantities matter?

That leaves one conundrum as I see it . What is the correct ratio for rotary processing? If 50ml is the min then unless you use a bigger tank your ratio changes. So if 140ml is the correct amount for a 135 film in rotary processing then does the ratio drop to 1+ 2 and if it does what alteration does this make to the development time? Here's what Ilford says

Rotary tube processors Rotary tube processors have very similar processing conditions to spiral tank processing by hand, except they process with small amounts of solution using continuous agitation and can be pre-programmed. ILFOTEC DD-X developer can be used to process films in rotary processors using recommended dilutions at 20°C (68°F).

So what does this mean? What does Ilford mean by "recommended dilutions at 20C ? I am unsure

So in summary 50ml of concentrate appears to be the correct minimum by my reckoning and for 135 film that always worked for me but is this wrong and I used to just "get away with it" by sheer luck or is 62.5 ml correct but the extra 12.5 ml makes only a marginal difference such that some might see it but others, more easily satisfied like myself, just failed to notice?

Remember I think I used to use the same 1+4 ratio for 120 film and never developed 2 x 120 films together so I did use more than was required for 120 but I can't say I ever noticed a difference between the look of the 135 negs and 120 negs so I did appear to be wasting the DDX concentrate

I hope this helps but I recognise that I also ask some questions to which I have no answer. Perhaps others do

pentaxuser

Mirko from ADOX mentioned this on several occasions: do not use rotary continuous agitation with B&W film. You compress the tonal range by doing this. B&W developers exhaust themselves in the dense areas and naturally slow down the development process, while continuing to be active in the shadows, creating a bit of compensating effect. Rotary doesn't.

I am just a messenger here, just parroting what I have read. Logically this makes sense, the same mechanics exploited by stand development is at work here, just to a lesser degree. I have never spent any time comparing two agitation methods in a controlled experiment.

A quick google search reveals that "continuous vs intermittent" is one of those topics, similar to pre-wet or not.

McDiesel said:

Mirko from ADOX mentioned this on several occasions: do not use rotary continuous agitation with B&W film.

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Hmm, So I should throw away my ATL-2?

I've used a Unicolor film drum off and on for maybe 40 years, I've never noticed any issues with "compressed tonal range." I reduce development by 20% from the times I normally use with a standard SS or Patterson tank. Using the same logic all of the big papers and wire services of the day should have not used a continues film process such as a Versimate.

Look, before we start arguing for or against this advice, please admit that "I never had problems" or "I get great results" are not acceptable because words like "problems" or "great" are relative and subjective. I hope I sound reasonable here.

Find some time to shoot a test roll with a properly constructed test scene (multiple exposures of grey card will probably be easier), then develop using both methods with a development time adjusted to same contrast. Then measure what you get with a densitometer and compare. Repeat for multiple film+developer combinations. Another route is to become a trained photo engineer. And only THEN you will be in a position to have an informed opinion on this matter.

I am too lazy to do neither of those things, so it's easier to simply listen to the CEO of a photochemical company

McDiesel said:

I am too lazy to do neither of those things, so it's easier to simply listen to the CEO of a photochemical company

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Sometimes there is little choice but to do this but usually there exist other "checks and balances" and often it is worth trying to find them. Lots of people in the 60s followed the same maxim as above when it was the CEOs of tobacco companies or more recently fossil fuel companies and the fast food industry in the form of CEOs usually has similar irrefutable evidence that there is no link with what they sell and obesity


It is not always possible to do this but the detective's ABC is a worthwhile philosophy to try and follow: Accept nothing; Believe no-one; Check everything

pentaxuser

McDiesel said:

Mirko from ADOX mentioned this on several occasions: do not use rotary continuous agitation with B&W film.

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This seems quite strange given that for decades Kodak has provided, without qualification, rotary processing advice in their datasheets for their developers and films. This is advice to all segments of the market, including commercial, educational and hobbyist.
There are some concerns, with some developers, about increased potential for oxidation of the developer, but no concerns about the images on the film.
Of course, all motion picture films - colour and black and white - are designed to be developed with continuous agitation. And as far as I know, all Kodak and Ilford films are quite happy being developed in commercial machines that use roller processing, and therefore experience continuous agitation in all the chemicals.
I'm afraid you are going to have to link to the source of what is clearly unusual and unexpected advice from a much smaller and less experienced and far less resourced player in the industry about the unsuitability of rotary processing for black and white film.

A little sensitometry will answer the question without a doubt.

If you intend to develop by time and temperature according to published times, read about and try to go along with all the relevant advice (which is intended to ensure consistency and successful results).

That includes the stock solution expiration date and shelf life when mixed in full stoppered bottles.

Follow the recommended stock solution per unit of film too.

But if you want the world to bend to you, then make some test exposures and develop the way you want to and then adjust development time until you get the results you want.

That’s a lot of words, but if you want to use less stock per unit of film and you want to develop with continuous agitation, (they may cancel out), find your development time by measuring the densities of developed test exposures (sensitometry)

You may find that your developing time is longer than anyone else’s- for example 13 minutes instead of 9. But that’s about the difference. Less stock developer, more time for the same results.

@MattKing well, let's try to think from the first principles here. Does continuous agitation save time? Yes it does, and time is money for commercial labs, so small sacrifice in quality is not a problem. Labs do lots of things that trade a bit of quality in exchange for efficiency/throughput. So it seems logical that Kodak and others would provide continuous agitation guidance to their most important customers.

Another angle to consider is that reduced agitation paired with extended time does indeed affect the curve. Exhausted developer indeed becomes less active in exposed areas. The obvious example of that is stand processing. I hope no objections here? Why then wouldn't the same principle apply to intermediate agitation, just to a lesser degree?

Mirko's argument checks out against thinking from first principles. I am yet to hear a single argument of comparable quality for continuous agitation. My gut also tells me that the difference between agitation methods will probably depend on a developer, and the difference itself could be quite small.

That said, @Bill Burk is right of course, "A little sensitometry will answer the question without a doubt."

McDiesel said:

Another angle to consider is that reduced agitation paired with extended time does indeed affect the curve. Exhausted developer indeed becomes less active in exposed areas. The obvious example of that is stand processing. I hope no objections here? Why then wouldn't the same principle apply to intermediate agitation, just to a lesser degree?

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Yes - in general reduced agitation is deleterious, leading to mid-tones that are flat and poorly rendered, resulting in negatives that are "yech" (that is a technical term).
Reduced agitation is a special purpose technique that can rescue you in certain very specific circumstances. Printing reduced agitation negatives optically is usually a challenging exercise that almost demands special purpose techniques like split contrast printing.
Post processing scanned images from reduced agitation negatives is something I dislike.

@MattKing instead of unprompted lectures on a random keyword in my thinking, you could have responded with an honest "I don't know". Admitting this on a daily basis is a healthy habit to have.

Mirko presented a logical argument against continuous agitation, nobody else on the other side delivered. And therefore, by the supreme rules of logical reasoning and common sense, I proclaim rotary processing for B&W film to be inferior.

Also, apologies to @logan2z for hijacking the topic. I'm gone now ...

McDiesel said:

Also, apologies to @logan2z for hijacking the topic. I'm gone now ...

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No worries, interesting discussion.

MattKing said:

Yes - in general reduced agitation is deleterious, leading to mid-tones that are flat and poorly rendered, resulting in negatives that are "yech" (that is a technical term).
Reduced agitation is a special purpose technique that can rescue you in certain very specific circumstances.

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Can we take it Matt that you are making a distinction between Kodak and Ilford recommended inversion agitation regimes and what you term "reduced" agitation?

Roughly at what level of reduced agitation does the "yech" arrive?

Thanks

pentaxuser

pentaxuser said:

The thing about 62.5ml is that if this is the minimum required then why does Ilford give the following table on page 2:

Tank Size (ml) Dilution 1+4 Concentrate / Water 100 20/80 150 30/120 200 40/160 250 50/200 300 60/240 350 70/280 400 80/320 450 90/360 500 100/400 600 120/480 700 140/560 800 160/640 900 180/720 1000 200/800 2000 400/1600

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Good question, I've emailed Ilford for clarification.

logan2z said:

Good question, I've emailed Ilford for clarification.

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I look forward to seeing its answer or your summary of it, should you want to share it

pentaxuser

McDiesel said:

@MattKing well, let's try to think from the first principles here. Does continuous agitation save time? Yes it does, and time is money for commercial labs, so small sacrifice in quality is not a problem. Labs do lots of things that trade a bit of quality in exchange for efficiency/throughput. So it seems logical that Kodak and others would provide continuous agitation guidance to their most important customers.

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Hi, I think you haven't carried your thinking far enough along, with respect to "time saving."

Consider the situation of a cine processor, the sort of machine I'm most familiar with. We ran some such machines with 35mm C-41 process at 50 feet/minute. These are "continuous" machines, which are fully strung with "leader" before and after processing film. When you start up processing, the film is attached to the leader, and the leader guides the film through the machine. Each roll of film is successively attached to the previous roll, and on and on. At the end of processing another leader is attached to the tail end of the film, such that the machine ends up fully strung with leader. So it is ready to go for the next production run.

So if we ran such a machine for say, 6 hours, it would feed in 50 X 60 X 6 = 18,000 feet of film - a bit over 3 miles. Now, the output side doesn't start until the first film goes entirely through the process, say 20 minutes or whatever it is. So every time it's started there is an "overhead" of 20 minutes added to the total production time. But aside from that, it's another 50 feet of processed film every minute.

Now, to your point about the effect of a longer developing time. Let's say that the C-41 process HAD BEEN designed with a one-minute longer developing time. Well, the machine would have been configured with a longer length of film in the developer, in order to run at the same speed. So still, 50 ft/minute of output, minus an extra one minute of output per startup. So we would have lost only 50 feet of processing in a day, or whatever. OR... the operators could just stay one extra minute.

Going to a more typical machine, such as a minilab roller-transport processor, the situation is basically the same. You don't lose a minute on every roll... you only lose a minute on the initial startup.

Now, if someone is running a hand tank, or a Jobo-style machine, for example, then yes, they would lose the extra minute for every time the tank was loaded. But that's not the sort of thing the photofinishing industry was built on.

Regarding the "quality" of the processing, "real labs" have always hated to give up quality, except from the standpoint of how much is the customer willing to pay. So historically the customers have always controlled the quality, at least indirectly. The outfit where I worked once owned the largest chain of one-hour labs in the US. The original plan was to have a couple of well-qualified techs at each store. But once lower-priced labs started to open up, we'll, that became the competition. It doesn't take long before the higher-priced techs are a liability, etc. That's really how the business went. Once the big-box stores started putting in one-hour labs, well... they didn't need to make a profit - they were bringing captive potential customers into their stores for an hour. So again, the customers essentially voted with their wallets as to how much quality they were willing to pay for. (My outfit eventually gave up and got out of one-hour lab business.)

pentaxuser said:

I look forward to seeing its answer or your summary of it, should you want to share it

pentaxuser

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I've exchanged three emails with them already and still don't have a clear answer. Still working on it...

pentaxuser said:

Can we take it Matt that you are making a distinction between Kodak and Ilford recommended inversion agitation regimes and what you term "reduced" agitation?

Roughly at what level of reduced agitation does the "yech" arrive?

Thanks

pentaxuser

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The critical factor that I referenced in my comment was "developer exhaustion, which I interpreted to mean "localized developer exhaustion".
"Reduced agitation" schemes that bring developer exhaustion into play do not include the Kodak or Ilford recommendations - developer doesn't exhaust locally if you are agitating once every 30 seconds or 60 seconds, unless you don't have enough developer activity in the tank in the first place.
Localized developer exhaustion is an important factor to consider with stand and semi-stand schemes.
If developer exhaustion hadn't been brought up in the first place, and the discussion had instead referenced the subtle differences between the results obtained with continuous agitation vs. intermittent agitation, I'm happy to participate.
The only meaningful differences I've observed between the results of continuous agitation and the sort of frequent agitation schemes recommended by Ilford or Kodak are the need to slightly adjust development times to match contrast.
Personally, I agitate continuously for the first 30 seconds (on a roller agitator) and then use the Kodak every 30 second scheme to hand agitate thereafter. I then use the roller agitator for all the rest of the steps.

Thanks Matt for the reply. Strange as it may seem, I am sometimes at least only looking for clarity

pentaxuser