Pushing film?


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Sep 10, 2011
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Chicago, IL
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I'm just getting into film. I've read that some people will 'push' iso 400 film instead of using iso 800 film. Is this recommended? Does this mean I should shoot the 400 film at 800, or let the film be underexposed and have the lab push it?

If you shoot 400 film at 800, it will need to be 'pushed' in the darkroom or else it will all be underexposed.
In a pinch, can one get by with this with minimal loss of quality? I suppose it depends on the DR of the particular film?
When you push, you are under exposing and over developing.

So, in your example, to push 400 ISO film to 800, you would set the ISO on your camera to 800 and then just shoot like you had 800 ISO film in it. When it came time to develop it (which you'd ideally be doing yourself...), you basically just develop it longer. How much longer depends mostly on how many stops you pushed it, and which developer you're using. One stop isn't much though. A one stop push doesn't even require any compensation when using T-Max film in T-Max developer, for example...

Some films push better than others though.
Pushing tends to increase contrast, in addition to allowing lower light shooting. This may or may not be a good thing, but is a side effect to keep in mind.
Push processing is not at all difficult. All you do is put the canister on the edge of a table and push it over. The higher you push it, the faster it will go until it reaches maximum velocity - thus, faster the film. You can actually do this several time over, and get ever faster film. This is a result of the interaction between the energy held in exposed film and gravitational velocity as predicted by Albert Einstein.


Now, for some non-BS.

The problem with push/pull is that it's not a linear reaction, so you can't just double the processing time and half the exposure and get similar results as if you used a film that is twice as sensitive. Also, while at any given density you can accurately predict how the film will respond to increased development time, this too isn't linear over all densities. Higher densities with greater exposure tend to develop out more rapidly than areas of lower density, resulting in a tendency to blow highlights, but with shadows that haven't developed to the same extent - in fact, this is the basis of Adam's Zone System method.

I also have found that push/pull exaggerates all other factors. If the water is slightly warmer than 20 degrees while pushing, the film will be pushed further than if it was slightly warmer at normal development. If pulling, the same is true of cooler water. So it's more important to get everything precise.
Pushing film has very little benefit in the shadows, as unpopular says. You will get more shadow detail exposing ISO 800 film at 800 than exposing ISO 400 film at 800 then pushing. With colour neg film I don't usually bother to push process for less than a two stop push, after 'underexposing' about a stop and two-thirds or so. If I have only underexposed by one stop I don't alter the processing. Different matter with B&W neg or colour reversal.

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