Pushing and pulling films

By Nelson Tan

Imagine this scenario - you have been shooting the entire day, and everything seems just great. The weather has been very co-operative, with deep blue skies and a cool breeze. There were plenty of photo opportunities around, and you snapped happily, and noticed that you had sufficient shutter speeds even though you stopped down to f/11 for greater depth of field. In fact, the shutter speeds were unusually fast for that aperture setting. As you sat down for a break after an entire morning of shooting, you casually glanced at your camera. To your horror, you found that your ISO setting was wrong ! You were using ISO 100 film, but you have set your camera to ISO 400 ! No wonder you were getting those great shutter speeds.

What do you do now ? Your images for the entire day were 2 stops under-exposed. Is there any way to get your images back ?

Yes. By altering the processing time, you can salvage your images to a certain extent. Using the processes called pushing and pulling, you can obtain usable images from over-exposed or under-exposed films. This article covers the basic aspects of these techniques. If you are very interested in knowing more about the effects of pushing and pulling films and other aspects of film, there is a more advanced article - Film Dynamics

What is pushing and pulling ?

Pushing and pulling is what building owners do to insult us, by telling us how to open the doors.

Seriously, pushing and pulling are lab processes where you alter the film's processing time to compensate for overexposed or underexposed films.

First, let's go through some basic terminology….

ISO is the speed of the film, such as ISO 100 or 400. But the speed you shoot at is called Exposure Index (E.I). So if you shot a ISO 100 film at the ISO 400 setting on your camera, you have exposed a ISO 100 film at E.I 400.

What are the effects ?

By pushing or pulling the film, you try to correct for the error in exposure, so that you end up with a image that looks normal, as if you shot with the correct film setting. However, there is no free lunch in this world. By pushing film, you end up with images that are more grainy and more contrasty than usual. Also, you pay around 50% more for the processing.

Why do it ?

There are two likely scenarios where you need to push film:
1) You have accidentally set the incorrect ISO setting on the camera, and so have to push the film to get the correct exposure.

2) You have only slow film, and need more shutter speed to capture the movement of the subject. You sacrifice the grain to get the image.

For example, in low-light situations like the this shot of the interior of a Thai temple, you might only have ISO 100 film which will give you a slow shutter speed and run the risk of camera shake. Rather than not being able to get any sharp pictures at all, you might choose to sacrifice fine grain and push the film by 2 stops to EI 400 so that you can at least end up with a grainier but sharp image.

How do you do it ?

Pushing:

Let's say you shot a ISO 100 film at EI 400. So what you have done is that you have underexposed the film by 2 stops. What you need to do now is to tell the lab that you want to push the processing by 2 stops. Or if you don't know how to calculate the number of stops, just tell them what you did and they will do the calculations for you.

Pulling:

If you exposed ISO 400 films at EI 100, you have overexposed the film by 2 stops. So just tell the lab to pull the processing by 2 stops.

Special points to take note:

Pushing or pulling affects the whole roll of film, so if you have exposed half the roll correctly and underexposed the other half, you are basically going to lose half the roll no matter what you do !

For example, you exposed half a roll of ISO 100 film at EI 400 before you discovered the error and corrected the film setting to finish shooting the film, you have half a roll underexposed. So if you ask the lab not to push, your first half will be underexposed. If you ask the lab to push by 2 stops, your second half of the film will be overexposed.

Moral of the story - if you discovered that you have shot the film at the wrong speed, continue shooting the film at the wrong speed and push/pull the entire roll !!

(Once, I asked a guy what he would do if the above situation happened to him, he gave me a smart-ass answer that he will tell the lab to push 1-stop. What a loser… he'll end up with 18 over-exposed images and 18 under-exposed images...)

The second point to note is that - pushing and pulling applies more to slide films than to colour prints film. Why ?

First, colour print films have greater latitude than slide film. This means that it can deliver useable images even if the exposure is out by 2 stops. On the other hand, if you wrongly exposed slide films by even 1 stop, the effect is very obvious. And unlike print films where you can correct for exposure during the printing process, there is virtually no way to work out anything with a improperly exposed slide.

Secondly, colour print films have slightly different film structure compared to slide films. They do not react in the same way as slide films. When print films are pushed, they may develop weird colour casts which are difficult to correct away.

Thus, pushing and pulling are more suitable for slide films than for print films.

Who does it ?

Don't bother going to your neighbourhood colour lab and ask "Hi... please push this film by two stops…" I'd be surprised if they understand what you are talking about. Push and pull processing are the domain of more advanced labs which are capable of more than churning out your birthday parties photos on automated machines. The process needs special timing and may contaminate the chemicals if not monitored properly. So only request for this service at the more professional labs.

So now you know the basics of pushing and pulling films. If you are interested to find out more about the process of push/pull, and other characteristics of film, you can read a slightly more advanced article on Film Dynamics.