variations in C41

I'd like to ask someone knowledgable in film chemistry to tell me what

possible specific variations (not counting push/pull processing) in

development process could affect which aspects of color negatives

(saturation, contrast, grain, sharpness etc.)

In other words, which chemical or physical variables of processing

affect which properties of the image?

Paging Ron Mowrey...

 

Seriously though, you might want to check the archives of the colour forum at www.apug.org, where this topic has been extensively discussed (in great chemical detail) by Ron and others.

Edgar, are you wantng to mix your own c41 ish formula or is this more of a gee whiz nice to know that approach? Ron is the expert as he worked for big yellow as a resercher for years and a couple of other pnetters make there own C41. Good luck

 

I am just curious in the fact that c-41 has standard time/temps that are made so as to not effect color shifts and such and was wondering what you want to muck with it.

 

I use the tetenal kit about once a week.

 

,Grinder

I don't want to do anything

 

I'm just asking to better understand the C41 process, and to know more specific what can go wrong with my negs when I give them to a lab and why.

 

I'm just currious

Jordan can you remember the title of the thread?

Read the process control section of Kodak publication Z-131 (http://www.kodak.com/global/en/service/Zmanuals/z131.shtml), which is Kodak's documentation of how to do C-41 processing and keep it accurate.

 

It shows why you need someplace that hires people who can be trained, and trains them well, to do your C-41 processing. Otherwise the H-D curve of any of the three color emulsions can be out of whack, not to mention retained silver problems.

 

What can go wrong? Aside the obvious idiot things of putting the wrong stuff in the wrong tank, temperatures can be off, times can be off, the replenishment rates can be wrong, the bleach can be overused, the bleach can be under-aerated, etc.

Agitation, time, temperature, pH, etc. Everything has some impact on contrast and speed not to mention grain and sharpness.

 

Other mfgrs processes have a big effect as well. There was an article in the old Darkroom Techniques that compared 6 different kits for sensitometry.

 

So, each kit and each set of individual variations will offset results from the product release aim, possibly for one or possibly for each characteristic. What disturbs me is that people eyeball the result or make a simple print and then make a judgement and say "this is ok" or whatever, but if they looked at it critically with a 'check' in the real C41 process they might see a huge variation.

 

I have run side by side comparisons and tested sensitometry, grain, sharpness and the whole gamut of color reproduction. Some variations look good on a single stimulus basis but are pretty sorry nonetheless.

 

BTW, my color tests include the original color produced by the negative and the color produced by the print from the negative. These are not always the same.

 

Ron Mowrey

I assembled the whole Z-131 manual into a single PDF binder; and it's available on my home page at:

http://users.snip.net/~joe/default.htm ...You'll also find the E6 manuals there as well.

 

Notwithstanding what Ron wrote above, the C41 process lends itself to minilab "tolerances," since corrections are applied in the printing process (ugh!)

 

QUESTION FOR RON: What is the tolerance for the orange masks? In the same batch in my Jobo, some are orange, while others seem bronze to brownish.

Regarding the masks, if you have the same film in the same process, the mask should be identical in color and density. If it is not, then there is something wrong with the film most likely or the process. Brownish coloration tends to indicate either silver retention or fog.

 

From film to film, the mask can vary as the dyes have to be adjusted for the proper correction. So a 200 film and an 800 film will differ in mask color and density. The speeds of the emulsion layers are tweaked to retain the proper color balance of the film as the mask color varies so that printing will come out to use about the same color balance.

 

Among processes, there is a release aim for film and for process regardless of the size of kit or type of kit that EK makes. This is not the same as a Fuji release aim, but is close. I have seen films that were identical in authentic C41 go in wildly different directions when processed in other C41 compaitble kits. I have seen the same thing with the old Ektaprint 3 process and work alikes. I have not tested it with the current papers and RA developer.

 

So, just about anything can happen between the film and process, but they are more carefully characterized and known by Kodak and accounted for as much as possible in the manufacturing process of both the film and kit.

 

For example, a pH error (down), agitation error (down) or temperature error (down) in authentic C41 introduces a known and precise decrease in contrast, speed and interimage color correction, and it takes place in each individual layer at a known rate. To be more specific, a lowering of pH might affect contrast just the same as lower agitation, but in the former case the yellow layer might go down faster and in the latter case the cyan layer might go down faster. This would change the order of color crossover.

 

Ron Mowrey

Ron, I'm getting wild variations in orange mask in a single (Jobo drum) processing batch when different films (mostly Fuji, some EK) are run. Of course, I'm not seeing any edge-to-edge variation, so chemical distribution isn't an issue: In fact, since I run a replenished line, I always pump in the max volume I can stuff in the drum.

Dan, I would run a locked beam set of prints from a beam adjusted for a good standard print you know is good. Then look for variations in density and color balance in these prints.

 

This will give you some indication of the effects going on. As far as standard Endura paper is concerned, the mask in dmin areas is a white or neutral density. If something is wrong, it will offset color balance or density between othewise normal negatives. A standard picture of a MacBeth chart would do well, because this will include color patches.

 

Ron Mowrey