If you are a film photographer, you no doubt realize the limitations you face when using a roll of film. Once it’s loaded, you really need to finish it before you start a new one.
The ISO restricts you to shooting in one lighting condition. Being able to ‘push film’ allows you to trick your film into thinking it has a higher ISO.
ISO in Film Photography
ISO in film photography is very important, perhaps even more important than with digital systems. The difference is that the ISO film speed comes with the film, and not with the camera.
With digital camera systems, you are free to change your ISO as you see fit. A digital camera can photograph very well lit situations, and then immediately change for low light situations.
This is all without the need for additional materials or devices, and it happens within a few seconds. With film photography, this isn’t possible.
A 35 mm camera is really only as good as the film you use with it. If you are shooting a well-lit scene, you would use a low ISO film speed, such as 100.
If you turn your attention to something indoors, your film speed isn’t fast enough to record any data. You are going to need a faster film.
So what happens if you don’t have any available? Does that mean you can’t photograph that scene?
Not at all, you just need to know about uprating your film and push processing.
What Is Push Processing?
Push processing is a technique for developing your black and white, or color film. It allows you to trick your film into thinking it is of a higher ISO than it actually is.
For example, if you have a very low ISO film, such as 100, yet want to photograph indoors, the 100 ISO film isn’t fast enough to capture the low light situation.
This environment needs a film with an ISO of 1600 or more. You can still use your 100 ISO film, but you need to ‘uprate’ it.
When you push your film during capture, you are ‘underexposing’ your scene. You are telling your camera that the film inside it is less sensitive than it actually is.
Most 35 mm analog cameras have a built-in light meter. Contacts inside the camera communicate with plates on 35 mm film, that tell the camera what ISO it is.
The camera adapts its light reading according to this value. Dials on the camera let you set the ISO value, in turn changing how your camera’s light meter works.
Changing this dial allows you to ‘uprate’ your film. This is telling your film it is much higher than it actually is.
If your 35 mm camera doesn’t have a way to communicate with the film, you have to use the settings yourself. For example, a 100 ISO film being treated as ISO 1600 is 4 times bigger.
This means, 4 times less light is needed for correct exposure. You’ll need to reduce your shutter speed, aperture or a combination of the two for four stops.
Uprating your film requires a ‘push’ process. This is because you need to push the ISO that you want to achieve. This happens in the development stage.
|Kodak TMax 400||TMax Dev||1+19||400||36.5||36.5||36.5||20C|
|Kodak TMax 400||TMax Dev||1+7||400||12||12||12||20C|
|Kodak TMax 400||TMax Dev||1+9||400||25||25||25||18C|
|Kodak TMax 400||TMax Dev||1+9||400||20||20||20||20C|
|Kodak TMax 400||TMax Dev||1+4||400||6.75||6.75||6.75||20C|
|Kodak TMax 400||TMax Dev||1+4||400||5.5||5.5||5.5||24C|
|Kodak TMax 400||TMax Dev||1+7||400||8.25||8.25||8.25||24C|
|Kodak TMax 400||TMax Dev||1+9||400||13.75||13.75||13.75||24C|
|Kodak TMax 400||TMax Dev||1+4||800||6.75||6.75||6.75||20C|
|Kodak TMax 400||TMax Dev||1+4||800||5.5||5.5||5.5||24C|
|Kodak TMax 400||TMax Dev||1+7||800||8.25||8.25||8.25||24C|
|Kodak TMax 400||TMax Dev||1+9||800||13.75||13.75||13.75||24C|
|Kodak TMax 400||TMax Dev||1+4||1600||8.5||8.5||8.5||20C|
|Kodak TMax 400||TMax Dev||1+4||1600||7.25||7.25||7.25||24C|
|Kodak TMax 400||TMax Dev||1+9||1600||13||13||13||28C|
|Kodak TMax 400||TMax Dev||1+4||3200||8.25||8.25||8.25||24C|
For example, look at the above chart. If we wanted to use Kodak T-Max 400 ISO film and develop it as it is (with a dilution ratio of 1+4), we would need 6.75 mins.
The same film acting as 1600 ISO would need 8 mins (+1.25 mins) and 3200 ISO becomes 8.5 mins. The longer process brings out more light in the film.
What Is Pull Processing?
If uprating your photographic film from a lower ISO to a higher one means push processing, then pull processing works in the opposite way.
You ‘downrate’ your film from a higher ISO to a smaller one. This happens when you have high ISO films but enter and photograph in a well-lit scene.
Consider the table below:
|Kodak TMax P3200||TMax Dev||1+4||400||6||-||-||24C|
|Kodak TMax P3200||TMax Dev||1+4||400||6.5||-||-||24C|
|Kodak TMax P3200||TMax Dev||1+4||800||7.5||-||-||24C|
|Kodak TMax P3200||TMax Dev||1+4||800||6.5||-||-||24C|
|Kodak TMax P3200||TMax Dev||1+7||800||13||-||-||24C|
|Kodak TMax P3200||TMax Dev||1+9||800||19.5||-||-||24C|
|Kodak TMax P3200||TMax Dev||1+9||1280||16||-||-||24C|
|Kodak TMax P3200||TMax Dev||1+4||1600||7||-||-||24C|
|Kodak TMax P3200||TMax Dev||1+4||1600||8||-||-||24C|
|Kodak TMax P3200||TMax Dev||1+4||1600||10.5||-||-||20C|
|Kodak TMax P3200||TMax Dev||1+4||3200||9.5||-||-||24C|
A Kodak TMax P3200 film developed at its native ISO, at a dilution of 1+4, would take 9.5 mins. When downrated to 1600, that number falls to 7 mins (- 2.5 mins).
If you go as low as 400 ISO, then the development time falls again to 6 mins (- 3.5 mins).
This is because the film doesn’t need to develop for the full amount of time to achieve the correct exposure.
Why Would You Want to Push or Pull Your Processing
The main reason you want to push your film is for versatility. It allows you to work by having one of two different, and small, ISO films.
With uprating and push processing, you can cover more than just well-lit scenes.
The other benefit is that you have access to higher rated films. With the removal of more and more films, we have less and less options.
Perhaps you really love a film, but it doesn’t come in other ISO forms, such as the JCH StreetPan 400. With this process, you can use it at ISO 1600.
There are some of us that want to achieve a higher grain amount in our images. Push processing forces more grain into your film as it needs to work harder to pull out those lights.
Pull processing and downrating your film gives you more control over the film’s quality.
A higher ISO rated film has more grain due to the increased size of silver halides.
If you downrate, you don’t need to use so many of them, so the quality increases. There just isn’t as much grain present on your final negative.
Again, you might love a film that only has high ISO options. By downrating, you can use it in well-lit scenes too.
Best Films for Pull or Push Processing
Black and white film is the best, most common and easiest film to push. As the push process increases film grain, it also increases the contrast in your scene.
This is actually one of the biggest reasons photographers use this ‘push film’ technique. Films Tri-X 400 & Ilford HP5 plus are great films to push.
Color negatives are the second most popular, as they can create slight color shifts from it’s increased contrast. You’ll also notice more grain. Try the Portra 400 & Fuji Pro400H.
Slide film or E-6 is the least common film for push processing. Yet, it can offer some great results. Like the color negative film, you can see an increase in contrast and subsequent color shifts.
Grain is more noticeable. Try the Provia 100f & Velvia 100.
For info on where to buy these films, check out this article on Where to Buy Film for Old Cameras.