Film and lens speeds are similar to shutter speeds. When someone refers to the speed of a lens, it refers to the smallest number f-stop the lens has. A lens whose smallest f-stop number is 1.2, for example, is “faster” than a lens with the smallest number of 5.6. This is because it has the ability to allow more light through the lens since it can open wider (remember, the larger the opening, the smaller the f-stop number).
Film that is said to be “fast” is film that requires less light for proper exposure. ISO 800 film, for instance, is a fast film. It is used for indoor sporting events or theater production photography, for example. In a situation where you can’t use flash or other extra lighting, you want to use a fast film.
Let’s contrast this fast film with traditional slide film with an ISO of 50 (like Fuji Velvia). This film is “slow”. That means that it trequires a lot of light to properly expose the film. You definitely need a tripod with this film! But, because of the characteristics of this film, you get very beautiful, saturated colors.
Let’s talk about how to figure out when and how to use combinations of lenses and film to get great results in various photographic situations. Let’s say you want to take pictures of your child at her dance recital. Obviously, you’ll be inside, and you probably won’t want to use flash. So, the question is “will there be enough light?” Maybe, maybe not. But how can you adjust for this situation?
We already discussed some variables that you can control as far as the existing lighting is concerned. In this situation, you will want a combination of a fast lens and fast film. A 400 speed film would probably be ideal, if your lens is fast enough. A 4.0 or 5.6 lens may not be fast enough. Refer to your user manual for your lens to see what speed it is. If you don’t have a fast enough lens, you can compensate with a faster speed film, like 800 speed. But be aware that the faster a film is, the more grain there is in the photo.
Now, let’s use another example, this time you are in Arizona, and the bright light is overwhelming. The shadows are intense, as are the highlights. What do you do now? First of all, you stop the lens down to its lowest setting, maybe f/22. There is more than enough light in this instance, in fact there is too much. So, combine a slow speed film with a small lens opening. You may even have to further reduce the amount of light coming in, with a filter. Polarizing filters are great in a case like this. Here is an interesting example of how polarizing lenses work.
We’ll get into filters in a later discussion…