Continuous vs Intermittent agitation - finding

[john_hicks]

Conventional wisdom and seat-of-the-pants educated guesses have it that in order to match EI and CI of films developed by standard intermittent agitation and continuous rotary agitation requires about a 10-percent reduction in development time when continuous agitation is used.

 

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I've found this to be _way_ off for two films.

 

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Background: I usually use intermittent agitation but I have this Jobo thing I somehow accumulated sitting over in the corner, so I decided to do some testing to find out what the development-time difference is.

 

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Jobo recommends a five-minute presoak based on their assumption that it'll give development characteristics similar to intermittent agitation. Phil Davis proved that to be untrue; he found that with such a long presoak different films shift characteristics virtually randomly. He also determined that a short one-minute presoak caused no significant differences in characteristics.

 

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So I set off to figure it out, using a one-minute presoak to avoid airbells, testing HP5+ developed in D-76H 1:1 and 1:3.

 

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The first test was with the usual 10-percent time reduction; the result was that I found the development time for a high-contrast EI 800 push, or about N+2 or so. So the conventional-wisdom 10-percent reduction is _not_ valid with this film and developer.

 

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Eventually I found that a 25-percent decrease in development time was required for an EI and curve match for HP5+ in D-76H at both the 1:1 and 1:3 dilutions.

 

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Also, again contrary to conventional wisdom, there's _no difference_ in curve shape resulting from continuous rotary agitation vs. intermittent inversion agitation. The curves virtually overlap from the speed point out 14 stops. This applies to both dilutions tested, 1:1 and 1:3.

 

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Tonight I ran the first test of Delta 100 in D-76H 1:1; results so far are that a 25-percent reduction in development time gives about N+1, somewhat higher contrast than desired.

[james___]

There is no substitute for testing. The conventional wisdom you speak

of isn't wisdom but false heresay. You should always test proceedures

and materials for get the outcome you want. Alot of this conventional

wisdom is no more than an attempt to be lazy and not do the testing so

important to the proper outcome. One mans 10% is anothers 20%. I use

constant agitation because I like the look of the prints. There is a

smoother tonal gradation and better internal contrast. And it is more

repeatable. You are right to test the two methods. James

[john_hicks]

Delta 100 turned out to want a 35-percent decrease in development time to match curves for continuous agitation and intermittent agitation in D-76H 1:1 and 1:3...and a couple of oddities appeared.

 

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When using intermittent agitation, the speed (defined as .10 DU above fb&f for Zone I) for D-76H 1:1 and 1:3 was EI 160, although I shot it at EI 100.

 

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With continuous agitation, it dropped to EI 100 in D-76H 1:1 and EI 80 in 1:3. That's 2/3 stop slower for 1:1 and a full stop slower for 1:3! Also, at the 1:3 dilution a mild shoulder appears beginning at Zone X.

 

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The same amount of stock was used for the 1:3 dilution for both the intermittent and continuous-agitation tests; no speed loss or change in curve shape was found with HP5+ in the same dilutions.

 

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So...for Delta 100 in D-76H with continuous agitation it appears that the 1:1 dilution is the sweet spot, with the 1:3 dilution reserved for those times when I have to deal with excessive sky brightness etc.

[jim_snyder1]

John,

 

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All good info. Thanks. Do you plan to do any testing with an

acutance developer and look at edge effects too? The 'conventional

wisdom' is that continuous agitation impedes edge effects while

minimal agitation maximizes them.

 

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Jim

[ed b.]

In response to Jim's last post, Richard J. Henry devoted considerable

research to the problem of edge effects and agitation in his

book "Controls in Black and White Photography." His conclusion is

that adjacency effects are caused by �lateral diffusion in the

emulsion layer� and are not affected by agitation.

[n_dhananjay3]

With regard to Jim's question, didn't Richard Henry report that he

found continuous agitation did not impair edge effects? That would

seem to suggest that edge effects are primarily due to movement

within the emulsion itself. I haven't seen any corroboration of that

anywhere else though.

 

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For what its worth, I did test the effect of dilution and agitation

on Arista 125 in HC110. I found that agitation did change the curve

shape over there - but only a small bit. Using continuous agitation

provided slightly increased contrast in the highlights (Zone VIII and

beyond) but I should emphasize that this was a small difference. I've

got much greater changes in curve shape by using a different

developer (like D23 to provide compensating development). Dilution

did not change the curve shape at all - different dilutions yielded

exactly the same effect as adjusting times. Extreme dilutions

resulted in some loss of speed.

 

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Continuous agitation did require an adjustment of time to compensate

but along the order of 35-40%. My times with 10 seconds every minute

were along the order of 6 mins. 6 mins with continuous agitation

provided about the equivalent of an N+2.

 

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Cheers, DJ.

 

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Cheers, DJ.

[john_hicks]

> look at edge effects

 

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I probably will once the current round is finished.

 

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If I recall correctly, Dr. Richard Henry found minimal effects of agitation on acutance assuming agitation was sufficient for acceptable evenness.

[jimvanson]

I'm kinda confused here as it was my understanding that continuous

agitation _did_ impair edge effects, thus sharpness. Anchell & Troop

write on page 31 of �The Film Developing Cookbook� Agitation may be

the least understood step in the development process...continuous

agitation...also increases the rate of development in the highlights,

suppresses the adjacency effects which enhance film sharpness...�.

Under the heading JOBO rotary processors (page 34) they go on to

say �Many photographers like to develop film with continuous

agitation in a JOBO rotary processor. Unfortunately continuous

agitation interferes with the formation of sharpness-enhancing edge

effects�.

Everything I�ve read except Henry�s "Controls in Black and White

Photography� seems to agree to this.

Isn�t agitation or more correctly minimal agitation in dilute

developers what Rodinal @ 1+100 or (T)FX2 and stand development is

all about.

I keep rereading the original post (good testing, John) and

thinking �what am I missing�.

[john_hicks]

> Unfortunately continuous

agitation interferes with the formation of sharpness-enhancing edge

effects�.

Everything I�ve read except Henry�s "Controls in Black and White

Photography� seems to agree to this.

 

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To me the big difference is that Dr. Henry documented his experiments in such a way that potentially anyone could perform the same experiment and confirm or refute his conclusions, while Anchell & Troop simply published assertions that may or may not have been backed up by experimental results. The problem with Anchell & Troop is that they usually didn't say so.

 

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For example, Anchell & Troop state that "Because continuous agitation exagerrates highlight development at the expense of shadow development it also results in lower speed and a shorter tonal scale."

 

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My experiment with HP5+ proves that statement dead false; the EI is the same and the curves are identical through 14 stops. I'd have to say that results are the same for each method.

 

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Otoh, the experiment with Delta 100 partially supports Anchell & Troop's statment; it did lose a little speed _but_ the curve shape is also the same through 14 stops.

 

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The curve shape for both films is pretty much straight through 14 stops; I can't imagine what they mean by "shorter tonal scale."

 

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So you see what I'm getting at? Dr. Henry provided experimental results to support his conclusions; Anchell & Troop may or may not have documentation to support their statement about agitation and edge effects. We don't know because no citation was given; for all we know they may have just been repeating common wisdom that a test wouldn't support.

 

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> Isn�t agitation or more correctly minimal agitation in dilute

developers what Rodinal @ 1+100 or (T)FX2 and stand development is

all about.

I keep rereading the original post (good testing, John) and

thinking �what am I missing�.

 

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I think you're missing the consideration of acceptable evenness.

 

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Dr. Henry adressed this, almost in passing, when he considered the McQuilkin method of agitation, a very minimal agitation method. He found that the McQuilkin method gave somewhat higher acutance figures than other methods but wrote, "the uniformity of development is the most non-uniform I have ever seen and, therefore, totally unsuitable for photography."

[john_hicks]

OK, last installment in this batch; Delta 3200 in DD-X.

 

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My goal was to find the appropriate continuous agitation development time for Delta 3200 in DD-X at EI 1600 to match my intermittent agitation results.

 

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The big surprise was that this film needed only 15 percent less development to match EI and curves.

 

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So...to sum up, looking at three films, two "core-shell technology" types and one a traditional-grain type, I found that the reduction in development time needed for continuous agitation rather than intermittent agitation ranged from 15 percent to 35 percent, that for two of the films the EI remained the same while one dropped to its ISO-rated speed, and that the curves are pretty much all the same within the 14-stop range tested. I'm thinking that for the one curve that showed a droopy high end, the causes were probably using too much developer dilution to cope with whatever development byproducts that film produced _and_ whatever extra aeration was produced by continuous rotary agitation.

 

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My next step will be to test a couple of sheet films in a Unicolor tank on a Uniroller and see if their development results match that of roll films in the Jobo.

 

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The purpose of all this is to reduce the number of errors in the process or iow, to reduce the "how come?" factor.

[fw1]

This is an interesting discussion. I've always assumed that there is

a correlation between edge effects and agitation ; i.e. the less

agitation, the more pronounced the edge effects, as the layer of

bromide at the edge of high density areas is removed by agitation -

this just seems commonsense. Now I'm wondering whether this really is

the case, although I have certainly noticed differences in films

where I have extended the development time and reduced agitation in

order to try to induce edge effects. Different film emulsions will

probably behave in different ways in this respect.

 

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John - you haven't mentioned temperature in all your tests above,

probably because you have ensured it is consistent between the

various tests, but I'm wondering if this could be one factor involved

in producing the development time differences you have found. Could

you please comment if only to eliminate this as a possible factor?

[david_oconnor1]

Just a note to say that I sure appreciated discussions like this one.

Since it is impossible to use the "Try it!" theory for everything,

the findings of learned experimentors is an advantage to us trying to

improve our craft. Thank you.

[n_dhananjay3]

John, another thought occured to me. It would seem to be the case

that there should be differences as a function of type of developer.

Slow developers are more likely to be limited by the speed at which

they develop the image i.e., any agitation (maybe even just

diffusion) will do the job of supplying enough fresh developer at

development sites since the rate of development would be slow enough

to be the limiting factor - agitation variations should prove less

problematic with these developers. However, agitation may be more

critical with rapid acting developers since the rate of diffusion may

not be fast enough to prevent local exhaustion. Thus, increasing

agitation with these developers should increase the contrast. Sound

logical? Cheers, DJ.

[john_hicks]

> haven't mentioned temperature

 

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I used 75F for all the tests. You're right that different temperatures could induce unexpected variations.

[john_hicks]

> should be differences as a function of type of developer

 

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Hmmm...I didn't see that in this round although I didn't directly compare developer types other than D-76H 1:1 and 1:3; it may be reasonable to consider the 1:1 dilution a more active type than the 1:3 dilution. In my tests the determining factor of how much compensation was needed was the film, not the strength of the developer.

 

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Presumably DD-X is a more active developer than D-76 but since I tested it only with Delta 3200 I don't know if the lower compensation required was a function of the developer or of the film.