Pushing and pulling film are techniques to get more out of the film than box speed allows.
Pushing means shooting and developing as though the film was a higher speed (ASA/ISO) than rated by the vendor. And pulling is the opposite, shooting and developing as though the film was slower than rated.
How this is achieved, is really simple. The film is either under- or overexposed by the number of stops required to achieve the desired film speed. E.g. by underexposing a 400 ASA film by one stop, you are actually pushing the film to 800 ASA – if you remember to develop the film as though it was an 800 speed film. And likewise, if you overexpose a 400 ASA film by one stop, you are pulling it to 200 ASA, if you develop accordingly.
This is possible because the latitude of a modern film emulsion is quite large – much larger than what we see in digital sensors. And most vendors will tell you, how much your film can be pushed or pulled while retaining an acceptable image quality. Typically about two stops over and under the rated box speed.
Now, this is quite cool, if you require a higher shutter speed, but lack the light when shooting at box speed – or require a shallow depth of field and a slower shutter speed for motion blur but have too much light. The downside is that you have to shoot the entire roll of film at the same ASA speed – if you want to develop traditionally that is.
This is where stand development comes into play. Stand development is basically a development method where you let the development tank “stand”, meaning you leave it alone for the majority of the development time.
For this to work, you need a thinner dilution of developer than usual.
I use a 1:100 dilution of Rodinal (R09 One Shot) for my stand development. I let it sit for about an hour, only agitating for the first 30 seconds, then stop and fix as normal.
Now, the theory is that, if you do not agitate, the developer will go to work on the highlights the fastest as they are the more sensitized. After a while the developer sitting next to the highlights will exhaust and “protect” the highlight areas from overdevelopment. The shadow areas, though, will continue to develop for as long as they need according to their individual levels of exposure.
Because stand development works this way, you can actually push and pull images throughout the entire roll of film and still have usable negatives on all exposures.
I did a small test to demonstrate that you can actually shoot one film at different exposures and get nice results on all images. The test is not perfect because the light changed a little because if moving clouds and I wasn’t on a tripod, so focus changes a little from image to image. The film is Ilford HP5+ box rated @400 ASA.
After scanning, I pulled the images into Adobe Lightroom and did an autocorrection on “0”. Then I synced the settings to the other four images, so you can see the immediate difference.
Below are the images in a larger size for inspection.