Black and White Photography

6 Film Exposure 


Film exposure refers to the amount of light that strikes the film when you press
the shutter button to take a picture. Correct exposure generally means letting
enough light enter the camera for the film to record the scene accurately. Too
little light reaching the film is called underexposure; too much light is called
overexposure. Both under- and overexposure can cause a range of problems and
prevent you from making a good or even acceptable print from your negative.
Arguably your most important technical challenge is learning how to expose
film. Once you understand exposure, you will be able to produce good negatives
consistently, and good negatives are the key to making good prints. This point
cannot be overstressed. With a good negative, you can produce a high-quality
print with relative ease; with a poor negative, you may never be able to make
even a passable print.
In this chapter you will learn about the factors that control film exposure, as
well as how light meters work and the various ways you can read light to establish
correct exposure. Finally, you will learn how to interpret and solve difficult
lighting situations.
There are many factors contributing to good film exposure. The key factors are
discussed in some detail in other chapters, notably subject lighting, lens aperture,
shutter speed, and film speed. Here’s a brief review.
Subject lighting. You will have to set your camera and lens according to the
subject lighting. In dim light, you will have to let in more light to expose film
than you will with bright light. While subject lighting is a critical element, you
can’t always control it. You generally have much more direct control over exposure
by adjusting the settings on your camera.
Lens aperture. The camera’s lens aperture is adjustable to allow more or less
light in through the lens to expose film. An f-stop is the measurement of that
opening. The larger the f-stop number, the smaller the lens opening. For instance,
a lens aperture set at f/11 lets in less light than one set at f/4.

Shutter speed. The shutter is a curtain that opens for a certain amount of time
when you press the shutter button to let in light to expose film. The shutter
speed is the measurement of that time interval. For most subjects, you will use
shutter speeds that are fractions of a second, such as 1/60, 1/125, 1/250, and
1/500. The faster the shutter speed, the shorter the interval and the less light
that reaches the film. For instance, a shutter speed of 1/500 lets less light in
than 1/60.
Film speed. Film speed refers to a film’s sensitivity to light—how much or how
little light is necessary to achieve correct exposure. The ISO rating is the