In digital photography, changing the ISO value is a matter of a few seconds, but what about analog? Each film is nominally produced with a specific ISO, less often with a small range (for example, 200–400). What if you need to set a different sensitivity when shooting? There are push/pull processes for this. You can get the result from another value!
What are push/pull processes?
ISO — expressed in numbers, the value of the film’s light sensitivity, its susceptibility to light. The higher the value, the higher the sensitivity. However, light conditions do not always correspond to the declared value on the coil. For example, film is rated ISO 800, but you’re shooting in strong lighting conditions, in bright, backlit sunlight. ISO 100 would be fine for this type of shooting. You can underexpose film in high light conditions, but get the desired ISO of 800 in development by doing a push/pull process.
By setting the ISO value in the camera settings, you also affect the shooting settings: a large ISO value can be compensated with a short shutter speed, a small ISO value with a long shutter speed.
Push process — this is an intentional underexposure of films with its subsequent re-development. In simple words: in your hands you have a coil with a nominal value of iso 400, and you have to shoot in poor lighting conditions. You can compensate for this with long exposures, but this is not always convenient. In this case, you can set the settings to the desired ISO 800: this will prevent long exposures, tell the camera that the lighting conditions are perfect, and the shots will not receive the proper amount of light in such conditions and remain underexposed and dark. This is exactly what the subsequent push process compensates for with a slightly longer film development. The frames in the final will not be so dark, and the information in the shadows will be preserved.
Pull process — this is overexposure of the film with subsequent underexposure. This process is reversed: let’s say you took ISO 200 film, but the day is sunny enough that you can set ISO 100. In this case, you overexpose the frames by letting in a little more light, shooting them at 100, and lowering the exposure by one stop in the developer . By developing at the original ISO 200, you can overexpose the film, resulting in light rectangles instead of photographs.
Why are these processes needed at all?
A logical question, given the ability to choose the necessary film based on the conditions of future shooting. However, these processes can have both a technical side and a creative one.
PUSH film development process
Key features: contrast increases, grain increases, color saturation increases, color distortion may occur.
Do not forget that changing the ISO value based on shooting conditions is easy only on digital cameras. In the case of film, sometimes you have to adapt to these conditions based on what is already there. Push-process allows you to compensate for short exposures in low light.
Secondly, the push process sometimes allows you to get a more interesting result in the pictures. With its help, the contrast of the image is enhanced, a pleasant graininess is added, and on color films it is possible to enhance some of the shades in the frame.
PULL film development
Key features: the contrast is reduced, the elaboration of details is improved, the color reproduction is more subdued.
The pull process helps to return the necessary detail. Only in this case when shooting with a lot of light, which threatens to overexpose. Pull will pull out details in the highlights and reduce the contrast of the picture. Secondly, the pull will make the picture softer, reduce the contrast and make the colors less bright, leading to pastel shades. A kind of stylistic device too.
What is important to consider?
• Theoretically, these processes are possible on any camera, however, technically, not on each. When applying the over/under exposure technique followed by a push/pull process, your camera should be able to manually control the ISO value setting. Almost every coil has a DX code, which is automatically read by the camera and based on which the camera sets the value. On many cameras, this parameter cannot be adjusted, while other cameras have the ability to enter the ISO parameter manually.
• Films are different. Push / pull process is not suitable for every one of them. First of all, this applies to color films, where the color can be greatly distorted during such development.
• Predictable results are possible with overexposure and underexposure within two values. No longer recommended. In the table above, you can compare the values and capabilities given, taking into account the resolution of a particular film.
• Best results are obtained on black and white films. They have a greater dynamic range and are more amenable to under or over exposure. In addition, films of the professional segment are more tolerant of push/pull processes, since they initially have a higher quality of the material to which this correction will be applied. Recommendations include Ilford HP5, Ilford PAN 3200, Kodak Tri‑X, and Kodak color Portra series.
• Be sure to indicate when handing over to the developer how many steps you need to make this or that process. This is important for the preservation of your frames and their competent development. If it is difficult for you to count, then just tell the employee what ISO value you shot at. Based on the nominal, this will help you choose the right developer and calculate the correct time to develop your film.