How to Develop Film Using the Push-Pull Process

Use what is known as push-pull processing to develop black and white film that was exposed at the wrong speed. This involves over or under processing film that has been over or under exposed. Although you can use the same process for slide film, it is not recommended for color film.

Difficulty: Moderate

Instructions

Pushing Film

1. Determine how many stops you have underexposed your film. For example, ISO 100 film shot at ISO 200 is underexposed by 1 stop. If it's shot at ISO 400, it's underexposed by 2 stops.

2. Push your developing time by about 20 percent for a 1-stop underexposure or 50 percent for a 2-stop overexposure.

3. Extend the print exposure time as an alternative to pushing the film, because pushing film affects the negative's contrast.

4. Increase exposure time, and you may get a grainier print or poor tonal quality. On the positive side, you may also get greater detail if you intentionally underexpose the film to get a greater depth of field and better shadow detail.

Pulling Film

5. Know how many stops you have overexposed the film. Exposing a roll of ISO 400 film at a setting of ISO 200 is overexposed by 1 stop. Exposing ISO 400 film at a setting of ISO 100 is overexposed by 2 stops.

6. Reduce the developing time by 10 percent for a 1-stop overexposure and 20 percent for a 2-stop overexposure.

7. Print images by cutting down their exposure time as an alternative to pulling the film.

8. Decrease exposure time for either negatives or prints, and you risk getting grainy prints.