Kodak agitation = "Tone devlopment equalizer" ?
I was always puzzled at how Kodak insists in its documentation on the small tank agitation of 5 inversions in 5 seconds every 30 seconds, versus everybody else's 4 inversions in 10 seconds every minute.
My conclusion is that Kodak wants to "equalize" development times.
What I mean is that given that in time X a certain film/developer combination will fully develop shadows, and given that:
- shadows don't change much with agitation
- shadows don't change much after they are fully developed
- Kodak assumes that people don't want to go into details, they just want to assume that time is directly proportional to contrast
then they will recommend:
- an official dev time of Y = 2 times X, or maybe Y = 1.5 times X
- strong agitation (5 inv/5sec/30 sec)
so that an average user will be able to:
- change contrast with slight changes in dev time (since highlights dev is maintained quick by the strong agitation).
- not run the risk of underdeveloping shadows (since they are already way past shadows dev time)
So this simplifies contrast management at the price of sacrificing further refinement in tone management.
Does my reasoning make sense?
The longer the film is in the developer, the more the shadows will develop, so it's false to say that having shorter dev times due to more frequent agitation will omit the risk of shadows that aren't fully developed.
I've seen this measured, so it's not some sort of magic or anything, just a dynamic of longer development time. This becomes practical if you photograph in high contrast lighting, or if you want to compress your tonal scale for some other reason, because if you slow down agitation to something like once every 3 minutes, or once every 5 minutes, you end up needing a longer development time. This becomes what we call compensating development, because it lifts your shadows while highlights are compressed, while mid-tones then become what you control with exposure.
I don't know why this is something that is omitted by every manufacturer out there, but was common knowledge and practice of many years ago. I guess that manufacturers want to stay away from getting too involved with people's processes, and give a standard recommendation that works 'pretty well most of the time' to be safe and not screw things up for folks. The recommended times, dilutions, and agitation patterns might give technically sound results, and yield a negative with a perfect tone scale, or whatever, but many people who use the film are less interested in technical perfection, and more interested in conveying something as abstract as emotion.
Agitation is a tool that we can use to shape our results, beyond the 'catch all' recommendation of the manufacturer, whatever it is. It helps us create a negative which results in a tonality in a print that lives up to our vision and what we want to convey.
Any recommendation from someone else, regarding what a developing cycle should be, should be taken with a grain of salt anyway, and only as a starting point where individual tweaks are then applied to get the best out of the light you're shooting in, the contrast of the lens you're using, your meter accuracy, your metering technique, the shutter accuracy of your lens, what paper you print on, and what paper developer you use, etc etc etc ad nauseum.
What manufacturers give you are recommendations. Not something you follow like some sort of gospel.
"Often moments come looking for us". - Robert Frank
"Make good art!" - Neil Gaiman
"...the heart and mind are the true lens of the camera". - Yousuf Karsh
The directions/recommendations provided by Kodak and Ilford are based on specific, controlled testing conditions, and are intended as guidelines for producing consistent, repeatable results and high quality image structure characteristics under average photographic conditions. It is unreasonable to expect comprehensive manufacturer instructions for alternative and/or extreme procedures. There are simply too many variables and subjective preferences involved. I'd also point out that in fact the recommendations from Kodak and Ilford will yield excellent negatives from a wider variety of photographic situations than people would have you believe. If people actually measured the results they get from the various procedures they employ, in many cases they'd find they are not getting what they thought they were getting.
It is difficult to generalize regarding the differences between Kodak's 30-second agitation intervals and Ilford's one-minute intervals. This depends on the type of developer and dilution.
In the context of most current films which have relatively short toes, it is not correct to assume the shadow densities remain stable as development time and/or agitation is changed.
5 inversions in 5 secs is getting close to the cocktail barman routine with a shaker and is very vigorous compared to 4 in 10 secs. Clearly the liquid's speed at 5 in 5 is much greater as well as being over twice as many inversions in the same time period as Ilford's. I wonder how much difference is made by (a) greater liquid speed and (b) twice as many inversions?
As far as I understand, shadows are not affected by agitation, only by time.
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I've experimented with standing development with highly diluted developer. HC-110 1:100 is great for shots that pick up contrast due to reciprocity failure. As far as I know, stand development works by the developer geting exhausted faster in the highlight than shadows. So at one point in the development, the shadows keep developing while the highlights are slowed or have even stopped development.
"Photography, like surfing, is an infinite process, a constantly evolving exploration of life."
This is not a correct statement. The purpose of agitation is to bring fresh developer to the emulsion and remove development by-products. The developer is exhausted more slowly in areas of lower density, but it will still exhaust. This of course depends on the type of developer and dilution.
Originally Posted by pierods
Have you done a test to compare the two methods? I believe Ilford gives recommended times for Kodak developers. In fact, looking at the data sheets for Ilford HP-5 and Kodak Xtol developer, they both recommend 12 minutes for HP-5 in Xtol 1:1 at 20°C while describing different agitation techniques for small inversion tanks.
Good point. Would the key here be the C.I. or Gbar that each manufacturer gives for its own inversion method? If each is the same or almost then it would suggest that the difference in the inversion method makes no difference or so little difference as to have a negligible effect on the negs.
Originally Posted by Greg Davis
I saw it described thus:
Expose for the shadows.
Develop for the midranges.
Agitate for the highlights.
I have learned to minimise agitation to keep highlights under control. I'm a slow learner but eventually by not following manufactuers' instructions to the letter in this regard has given me better prints.