Pushing film, and EI

frXnz kafka

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I've got a couple questions regarding film speed. I'm mostly concerned with black and white film, but I'm sure some of this applies to color film as well.

First, what is the difference between ISO and EI?

Second, let's say I'm using a 400 speed film, and I want to push it to 1600. What changes? I assume I'd change the ISO setting on my camera to 1600, but what changes in the development process? Is there a general rule of thumb for figuring out developing times, or is it more or less guess and check?
 

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EI stands for exposure index which is discovered by film testing, which is not guessing, but serious testing of film and development combination.

ISO is the speed that the manufactor has determined.

Pushing the film is going from 400 to 1600, and what really occurs is an increase in contrast with increased development times which is a by product of pushing the film.

You will need to increase the development times as you increase the ISO .

Rule of thumb is about 20=25% per each fstop of push.
What your really doing is allowing more options with your fstop or shutter speeds, which will allow you to get some image in very low light conditions. However, you must also increase the development times.
 
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frXnz kafka

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EI stands for exposure index which is discovered by film testing, which is not guessing, but serious testing of film and development combination.

ISO is the speed that the manufactor has determined.

Pushing the film is going from 400 to 1600, and what really occurs is an increase in contrast with increased development times which is a by product of pushing the film.

You will need to increase the development times as you increase the ISO .

Rule of thumb is about 20=25% per each fstop of push.
What your really doing is allowing more options with your fstop or shutter speeds, which will allow you to get some image in very low light conditions. However, you must also increase the development times.

So if I'm pushing 400 speed film to 1600, I should develop for about 40-50% longer?
 
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frXnz kafka

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frXnz kafka

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Well I developed a roll of Ilford HP5+ that I pushed to 1600 today. I haven't enlarged anything yet, but the contact sheet looks great. I think I might try to push a roll of 400TMax to 3200 next :D
 

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