Pushing film seems to be one of the topics that comes up often, both in the Little Bellows Facebook Forum as well as in my Embrace the Grain Workshop. In my workshop, I dedicate one whole week on pulling and pushing process. My students get to learn what these processes mean and how they affect your final image. We even get to talk to Belinda Olsen from The FIND Lab during one of the live office hours so we can understand everything from the lab's point of view.
One of the common misconception of pushing is that it adds "exposure" or "light" to your film. It cannot be further from the truth. Today, I want to take a this opportunity to explain what pushing film actually means by using easily understandable terms and by keeping it simple. But first, let's go back to the beginning:
When you expose a frame in your camera using shutter speed and aperture, you are creating a latent image on the negative that has potential for density. During the developing process, the latent image gains density in proportion to the sensitization by the exposure. When you look at your negatives, the part that's the darkest is the most dense, and the part that's the lightest is the least dense. Therefore, the highlight is denser than the shadows on a negative. So what does pushing have anything to do with this?
What is pushing? Pushing is overdeveloping an exposed film by submerging it in a developer or the chemical bath longer than a specific time given for that film speed.
During the normal development time, the density of each zone in The Zone System is reached to its exact density. For example, zone 5 reaches its exact density at 6 1/2 minutes. However, as the development time increases (over-development), the density for each zone also increases. The higher zones such as zone 4 and above will be progressively affected by over-development than the lower zones such as Zone 0 to 3. Here is a PERFECT visual example given in one of my favorite photography book, The Art of Photography by Bruce Barnbaum:
As the above visual aid showed us, the higher zones progressively get denser as the development time increases, and the lower zones are less affected by over-development. With the larger expansion between highlight and shadow, we say pushing in development results in higher contrast in an image.
Now that you know what pushing film is and how it affect the characteristic of the film, you should understand that when you "push" film, you do NOT "add exposure" to your film: the negative was already exposed to the amount of the light that was determined by the camera settings (Shutter Speed and Aperture). The exposure was already made. The overexposure or underexposure was done in camera even before the pushing process begins.
Let's put this concept in a real-life example:
When you rate a 400 speed film at 800 ISO, you are essentially underexposing your film by one stop. This underexposure is done when you click the shutter release to take a picture. There is no further work you can do to add "more light" or "more exposure" to a frame that has been exposed. However, you can compensate this underexposure by over-development or pushing to increase the density of the negative. Based on the visual example above, the lower zones such as zone 3 and below do not get affected by over-developing as much as the higher zones such as zone 4 and above. Thus, the more time the film is submerged in the developer, the more contrast you will get in your final image: the higher zones get denser while the lower zones are barely changed throughout.
I hope this helps explain how pushing film works. If you have any question, you are welcome to join me in Little Bellow Facebook Forum to learn more about the art of shooting film!
SOLD OUT! Registration for Joyce's online Intro to Film Workshop, Embrace The Grain, starts today at 9:00 am Central Daylight Time. Don't miss this opportunity to learn from the bests in film photography!