Push/Pull process, temp vs timing???
Posted 13 January 2009 - 06:56 AM
Posted 15 January 2009 - 07:43 AM
one — you have three separate color layers if not the double number with certain stock which are chemically affected one after the other through time (logically),
two— the layers will never react precisely in parallel manner, so we have to deal with color shifts,
three — speed, actually density developed out after a certain formula, depends primarily on the chemistry (the most complex variable of all),
four — exposure, in itself the product of light intensity and time, so a certain light amount, makes non-linear differences (Schwarzschild effect), and
five — temperature variations again do not always give linear changes.
Point four can be deleted in printing since exposure time remains mostly constant.
Point one is connected with point five.
Point two may be corrected for by densitometric evaluation and subsequent programing.
I think that the manufacturers tend to recommend everything standard, you know, along their guidelines and chemicals. Cinema projection calls for a standard print density. Lab managers speak Laboratory Aim Density, a Kodak invention. Directors and DP almost invariably want to move between the extremes, often without any knowledge of film projection physics. Worse even the electronically risen people.
Start studying this field of interest with a crisp black-and-white print in a theater. Check out what happens with you in high-key scenes and in low-key scenes. Then compare color imagery to it.
Posted 16 January 2009 - 02:58 AM
Posted 16 January 2009 - 04:29 AM
Well, generally there's the tendency towards the magenta layer to exaggerate with either pushing (prolonged developing time) or raising the temperature. This has been the top concern of Eastman-Kodak chemists with the older (and discontinued) color print films, I think it was 5384/7384. But that is an inherent issue as old as multi-layer colour film exists.
Is there one factor than affects this shift more than the other, like say if you process the film at a normal speed but increase temperature would that tend to instigate a color shift more so than keeping the temperature normal and reducing processing speed or vice versa?
Modern color film chemistry had to become balanced over so many factors. There is the p-H value, you know, proton concentration or acidity/alkalinity — very important, also agitation, and almost unknown: surface activity or better ion activity at the interface gelatine-liquid. It can make some difference whether the film enters the developing bath directly or whether it comes from an alkaline prebath such as it is still employed for the removal of backings. They are right now trying to do without a rem-jet soot gelatine backing layer.
Still I'm certain that you will master this all. Note everything like a donkey and learn from experience in your actual situation: water, machine, and so on.
Thank you for your faith.