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My question: in general, what results when color film is overexposed in-camera, then push processed in development?

I'm trying to wrap my head around color film exposure and development, and how each affects the final image. If overexposure of color film serves to provide more detail to shadows without blowing out highlights (because of the typically wide (over)exposure latitude of color film), and if push processing serves to increase film contrast without greatly affecting the midtones, does combining the two techniques provide a combination of the two effects? In other words, will the images have both some greater shadow detail due to the overexposure, but also an increase in contrast due to the push processing? What's the trade-off?

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    Just to clarify, you are aware that when you underexpose you are supposed to push the development or over developed to compensate for the underexposure, and vice versa when you overexpose you then pull the development or under developed to compensate for the over exposure? You want to overexpose and then over develop ? – Alaska Man Aug 30 '18 at 6:00
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Normally, push processing is used with underexposed film. The typical effect can be seen in the film, Barry Lyndon, nearly all of which was push processed:

enter image description here
Still image from Barry Lyndon

Overdeveloping the film grows the grains bigger, so that it brings out details in underexposed areas, and reduces detail in normally exposed areas.

If most of the image is overexposed to begin with, then push processing will reduce the detail overall. This will result in the image having a coarse, granular look with washed out highlights.

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    It doesn't technically grow the grain bigger; it is always the size they were at manufacture. But it does make the grain more obvious in the final print. – Jim MacKenzie Aug 30 '18 at 14:47
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    @JimMacKenzie If you examine BW negatives microscopically (which I have done), you will see that what are called "grains" are actually little clusters or agglomerative clouds of silver. When the film is pushed, these little clouds get bigger. – Clickety Ricket Aug 30 '18 at 15:18
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    Grain clumping, yes. It's not the grains becoming bigger per se, but rather that they clump and appear larger. I understand what you mean. – Jim MacKenzie Aug 30 '18 at 15:28
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    I think there is a misunderstanding of what a "grain" is. A grain is not a silver halide crystal, which is invisible. The word "grain" does not refer to a crystal, it refers to clouds of elemental silver which are suspended in the emulsion. These clouds are developed by the developer, an organic chemical that destroys the crystals and reduces them into globs of elemental silver. These globs are the "grains" that are seen when a photographic negative is viewed with a microscope. – Clickety Ricket Aug 30 '18 at 17:51
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Usually, one would want to push process film that was underexposed. For overexposed film, one would need to pull the processing to get 'proper' exposure.

Let's talk about push and pull for a moment.

When shooting film, if one exposes for a film speed faster than the actual speed of the film, one is technically pulling (underexposing) the film. The film then needs to be pushed in the other direction (over developed) when processed. But many photographers say they are pushing their film while underexposing during shooting when what they actually mean is that they are pulling (underexposing) their film when shooting because they intend to push (overdevelop) the film when processing.

On the other hand, overexposing the film when shooting it is pushing the exposure brighter. This needs to be counteracted by pulling the development time back to compensate.

Like many things in photography, it's about ratios and reciprocals. If I expose by giving the film three-halves (3/2) as much light as I should, I then need to develop the film to two-thirds (2/3) the typical development. If I expose the film to one-half (1/2) the 'normal' amount of light needed, I then need to develop it to twice (2/1) the 'normal' development. (Please note that development times are not linear - twice the development does not necessarily mean developing for exactly twice as long).

For instance, if I have ISO 100 speed film in the camera and choose to expose for ISO 400 speed film, I'm underexposing by two stops. It is true that ISO 400 film is more sensitive (and thus brighter) than ISO 100 film. But when I change my camera's ISO setting to '400' I'm not actually changing the film's sensitivity to ISO 400 - I've still got ISO 100 film loaded! What I am doing is reducing the amount of light the camera's meter says my film needs to be 'properly' exposed. So my film winds up underexposed by two stops.

When that film is developed, it needs to be pushed two stops brighter to get more or less 'proper' exposure. But the result will be lower contrast (brighter shadows) and coarser grain than if the film had been metered and exposed for ISO 100 and normally developed.

If you overexpose your film, you would normally pull process it by developing it for less time than normal. This will tend to increase contrast in the mid-tones and dark areas and muddy the shadows, but highlights that have been totally blown will not show detail, they'll just appear to be a uniform bright gray when printed.

If you push your film one stop when exposing (give it twice as much light as the meter calls for) and then also push your film in development (develop for longer than normal), you'll get a negative with very high density that will translate to prints (or scans) with a low contrast but washed out look with blown highlights if there were any in the scene and no true black areas.

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I am not a fan when it comes to pushing or pulling color film. Yes, I know these techniques can be beneficial, especially so if the camera exposure is known to be in error. That being said, old time black & white photographers often quote the adage,” expose for the shadows and develop for the highlights.” I never liked that axiom, but I often employed it. I do not like it because I know that in order to squeeze the full grayscale out of film, exposure and development must be spot-on. Any time you compromise, the grayscale withers. However, in art, there are no rules; you are free to follow your heart.

Color film is a different animal than black & white. I am mainly referring to the fact that modern color films sport several emulsions for each of the three primary light colors. As an example, they may contain a slow, a medium, and a fast red-sensitive layer, same for green and blue. Now, developing is partially an infusion process, whereby the chemicals must permeate into the gelatin binder to reach their target. To this end, the film’s hardness, the temperature of the solution, and the immersion times are carefully conceived. Violate anything, and the final color balance is distressed. The red emulsions are at the bottom of the strata; it takes longer for the developer to reach and act on them. Alter the developing time or the temperature, and the film goes red or cyan. Same for the middle green and the top red layers; they are inclined to go green-magenta and blue-yellow.

If it’s a one man show, this color balance alteration might not harm. The worst it might cost is a filter-pack shuffle or nowadays, a software correction. In the old-days it always induced pain because keeping color printers in topnotch balance is a daily inconvenience (hard work).

In any event, the results often justify the means. Experimentation is tricky. At worst, it will cause you extra time in the darkroom. Again, the full scale of film is achieved when everything is spot on. Increasing or decreasing developing time alters contrast as well. I say go for it.

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    I agree with you. Unless I am artificially trying to attain ridiculous contrast (and I could use lith film or printing to do this instead), I try to get the best negative I can and then go from there. – Jim MacKenzie Aug 30 '18 at 15:29
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    Thank you for pointing out the negative as an intermediary step. One can tweak colors and contrasts when going for a print. But if you have a less than ideal negative...life gets so much harder. – Hueco Aug 30 '18 at 16:11
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The best way to find out something new it’s to try it by yourself and see if the results are to your liking. Try different combinations and see if you ruined your negatives or you get something that you can use. Anyways you will learn by doing even if it seems to get you nowhere.

And don’t forget you can still play with the film while making the positive copies.

In photography there isn’t actually a right or wrong way to do things if you obtain what you want to get out of a picture.

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