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Push/Pull process, temp vs timing???


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#1 James Steven Beverly

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Posted 13 January 2009 - 06:56 AM

I would like to get a bit more detail on the push and pull processes and how timing and temperature manipulation separately and in combination affect the process. I'm trying to understand the relationship between speed, temperature and the effect it has and say how different combinations of speed and temperature will affect ti look of the image and which ones seem work better or if the look can have a manipulation not able to be created by just speed or temperature alone. Thanks-Steve B)
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#2 Simon Wyss

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Posted 15 January 2009 - 07:43 AM

Steven, this is one of the most complicated subjects. Why ?

Because
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.
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#3 James Steven Beverly

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Posted 16 January 2009 - 02:58 AM

Wow! :blink: Well that's the kind of stuff i was looking for. I knew it would be a steep learning curve but some of the points you mentioned I hadn't thought to take into account. For example, I pretty much sumized that time and temperature would be interconnected and there would be a overlapping of what each would do to the film being processed but it's hadn't occurred to me that the 3 color layers would react differently or that initial exposure would play as critical a role to the Push/Pill process as it does and to be honest even with all my reading on the subject of film processing, I had never heard of the "Schwarzschild effect". Now it MAY have been included in one or both of Dominic's Books, Film Technology in Post Production and/or Motion Picture Film Processing, but I either glossed over it or it just didn't register. Also, color saturation variables was something I expected but not color shift, however, now learning how the 3 color layers do not react linearly to changes in the Push/Pull process, I can see why color shift would almost be inevitable. 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? B)
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#4 Simon Wyss

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Posted 16 January 2009 - 04:29 AM

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?

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.

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.
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