Roger Hicks
Veteran
A lot of people talk about 'pushing' and 'pulling' films as if any deviation from the box speed were a 'push' or 'pull'.
It isn't. ISO speeds are determined sensitometrically (not in camera) and the film is developed in a stated developer to a standard contrast (gamma approximately 0.62). The film speed is based on the exposure needed to give a density of 0,10 above film base plus fog.
Develop to a higher gamma and you will lift the speed point: this is 'pushing'.
Develop to a lower gamma and you will depress the speed point: this is 'pulling'.
Develop to the same gamma in a different developer that gives a different speed and you are neither pushing nor pulling: you are changing ISO speed through developer choice. Fine-grain devs can knock 2/3 stop or more off the true ISO speed, so that an ISO 400 film drops to ISO 250 or less. Speed-increasing devs, often loosely though inaccurately called 'push' devs, can add 2/3 stop or a little more, raising an ISO 400 film to ISO 650 or better.
Of course you can also push or pull in these other developers: HP5 at EI 1000 in Microphen is about a half-stop push (small increase in contrast) while HP5 at EI 1000 in Perceptol would be more like a 1-1/2 stop push (bigger increase in contrast).
Merely rating the film differently is something else again. If you rate HP5 at 200 but develop to the standard contrast, you are not pulling: you are simply overexposing. This will reduce sharpness and increase grain size but you may prefer the tonality.
This is before you start considering equipment variations such as slow shutters and variations in lens flare, or variations in metering technique such as incident, spot readibng shadows, etc.
Why post this? Partly to clarify matters for people whjo don't understand the terms and partly as bait for my web-site, www.rogerandfrances.com -- take a look at the Photo School.
Cheers,
Roger
It isn't. ISO speeds are determined sensitometrically (not in camera) and the film is developed in a stated developer to a standard contrast (gamma approximately 0.62). The film speed is based on the exposure needed to give a density of 0,10 above film base plus fog.
Develop to a higher gamma and you will lift the speed point: this is 'pushing'.
Develop to a lower gamma and you will depress the speed point: this is 'pulling'.
Develop to the same gamma in a different developer that gives a different speed and you are neither pushing nor pulling: you are changing ISO speed through developer choice. Fine-grain devs can knock 2/3 stop or more off the true ISO speed, so that an ISO 400 film drops to ISO 250 or less. Speed-increasing devs, often loosely though inaccurately called 'push' devs, can add 2/3 stop or a little more, raising an ISO 400 film to ISO 650 or better.
Of course you can also push or pull in these other developers: HP5 at EI 1000 in Microphen is about a half-stop push (small increase in contrast) while HP5 at EI 1000 in Perceptol would be more like a 1-1/2 stop push (bigger increase in contrast).
Merely rating the film differently is something else again. If you rate HP5 at 200 but develop to the standard contrast, you are not pulling: you are simply overexposing. This will reduce sharpness and increase grain size but you may prefer the tonality.
This is before you start considering equipment variations such as slow shutters and variations in lens flare, or variations in metering technique such as incident, spot readibng shadows, etc.
Why post this? Partly to clarify matters for people whjo don't understand the terms and partly as bait for my web-site, www.rogerandfrances.com -- take a look at the Photo School.
Cheers,
Roger