Black and White Photography

4 The Camera Lens


The lens is one of the fundamental tools of photography. There are two main
types: camera lenses and enlarging lenses. The camera lens is located on the
front of the camera body and has several functions: It gathers light from the
subject you are photographing, allows you to focus that light on the film, and
controls the amount of light that reaches the film. It also determines how much
of the subject will be included in the picture and which parts of the subject will
be in or out of focus. You will learn about these controls in this chapter.
Some cameras have a fixed lens, one that is permanently attached to the
camera body. Fixed lenses are a common feature of point-and-shoot and other
snapshot-style camera models. They also are found on a few more expensive,
sophisticated cameras. Most fixed-lens cameras are relatively compact, but
have limited versatility.

Other cameras have interchangeable lenses, which offer a lot of creative

control. Interchangeable means you can remove the lens from the camera body

and replace it with a variety of other lenses for a wide range of uses. For example,

you might choose to replace your lens with one that’s better for lowlight

situations, close-ups, or shooting distant subjects. Cameras that accept

interchangeable lenses include the very popular 35mm single-lens-reflex (SLR)

models and medium-format SLRs, some rangefinder models, and view cameras.

There also are digital SLRs that accept interchangeable lenses.

When buying an interchangeable lens, note that compatibility is crucial. A

lens from one camera manufacturer usually doesn’t fit on a camera from

another manufacturer. Your best bet is to buy lenses made specifically for your

camera, either from the camera’s manufacturer or from an independent lens

maker. Many independent brand lenses are of good quality and relatively

affordable, but make sure you specify your camera model when buying any

lens to make sure it is compatible.

Whether fixed or interchangeable, all lenses control or affect these basic

functions: focus, film exposure, angle of view, and depth of field.

Probably the most obvious thing a camera lens does is focus—make the image

sharp. It does this by gathering the scattered light rays that are reflected by a

subject, causing them to converge on film to form the picture. Focus is

controlled by moving the lens elements (an array of small, specially shaped

pieces of glass or plastic inside the lens) to control where the light converges.

But you don’t have to understand optics to use your camera lens. On nearly all

cameras, the process is quite simple and intuitive. And most cameras provide

visual aids to help you focus easily and sharply.

Some camera systems offer manual focus only. Others offer autofocus (AF),

or automatic focusing, in which the camera and lens work together to do the

focusing for you. However, most autofocus cameras have a switch—sometimes

on the side of the lens, sometimes on the camera body—that allows you to

choose either manual or automatic focusing.

Manual focus is the simplest to understand, but not always the simplest to

use. When you turn a ring on the barrel of the lens, it moves the lens in and out

to achieve focus. With some lenses you can see the physical in-and-out movement;

others have internal focusing (IF), which means you can’t see the movement

because the focusing action happens inside the lens.

As you look through the viewfinder of most manual-focus SLR cameras, you

can actually see the subject become sharper when you turn the lens. Some

models have a focusing aid called a split-image circle in the viewfinder. As you

view the subject, you see a horizontally bisected circle in the middle of the

viewfinder. When the subject is out of focus, the image details depicted in the

top and bottom halves of the circle don’t align; when the subject is in focus, they

do align.

In most cases, autofocus is quicker, simpler, and more accurate than manual

focus. To autofocus, you point your camera at your subject so that the focus

point, usually indicated as brackets, boxes, or other marks in the center of the

viewfinder, covers the part of the subject you want in focus. Press the shutter

button halfway down to activate the focus, and then press the button all the

way down to take the picture. Sounds easy enough, but in practice autofocus

doesn’t always work as well or as quickly as you might like.

All lenses have an aperture, an opening created by a series of overlapping blades

that allows light into the camera. The lens aperture is adjustable on almost all

camera lenses. You can open it up to allow more light in, or close it down to

reduce the amount of light that passes through.

Film of a given speed (sensitivity to light) needs a certain amount of light, not

too much and not too little, to record an image. The size of the lens aperture is

one of two factors in determining how much light is allowed to reach the film,