Control Film Speed in Black and White Photography

Photographic control doesn’t end when you’ve pressed the shutter release. You can continue to exert control over the landscape image in the lab, in the developing tank, and in the home darkroom.

Many processing controls are simple, however it is not the same when it comes to changing of film speed. When we load a film with ISO400, then it is hard to change it to lower ISO setting of 100 or set it to higher ISO setting of 1600. You would have to finish the whole roll of ISO400 film first before changing to another type of film, and this is very inconvenient, especially if you have loaded the wrong film in the first place.

The good news is, it’s possible to boost or cut the speed of most slide films by simply increasing or reducing the time the film spends in the first bath of developer. Labs call this process “pushing and pulling”, and you can specify the speed change you need when you take the film in to be processed. Just tell the lab the number of stops by which you want the speed changed - you don’t need to know the new process times.

Why should you want to change film speed after exposure? There are many reasons: perhaps you inadvertently set the film speed dial to the wrong ISO number; or maybe you simply decided that the whole film would look better slightly darker than usual. Note, though, that the whole film is affected, and you can’t specify a speed change for just a few frames. If you are unsure what effect the speed change will have, ask for a “clip-test”. The lab will cut the first few frames from the roll, and process these in advance of the rest of the roll. Clip tests can of course be pushed and pulled quite independently of the rest of the film.

Some photographers use pushing and pulling to change other characteristics besides speed. Pushing film tends to increase grain size, and increase contrast, and these changes subtly alter the appearance of the landscape images. The changes are most dramatic when the base speed of the film is itself high, and the film is pushed two or three stops.

This versatile control over film characteristics is not available to users of negative film, but there are compensations. When printing negatives, it’s possible to shade parts of the print during the exposure, to increase shadow detail, and to give extra exposure to the highlights, so that they appear darker in the print. If you have access to a darkroom, these “local” exposure controls are easy to master, or alternatively you can specify them when instructing a lab.

Find out more things about Camera Photography and Tips To Take Photos. Check out Basic Camera Photography for more information.

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