technical: Lenses 1
 

Lenses

The lens of the camera is the part that allows light in to the film. Lenses consist of complex arrangements of high specification curved glass elements that can be moved further and nearer to the lens in order to focus the image.

If you are using a zoom lens or interchangeable lenses on a camera body, then it is useful to know which lens to use in which photographic situation, and how your choice will affect your picture. It is useful to know something about the sort of lens you are using, even if you just have one fixed lens.

Focal length

Lenses are classified according to focal length, which is the distance from the nearest element of the lens to the film plane, expressed in mm. All lenses except zoom lenses have a fixed focal length; zoom lenses have a variable focal length, which is useful as one zoom lens can take the place of several interchangeable lenses. The focal length is the most important feature of the lens to know about as this controls image size, and this will determine your choice of when and how to use the lens.

Standard lenses

For a 35mm camera the so called standard lens is 50mm. It is called the standard because the perspective it produces in the image is closest to that seen by the human eye. Sizes of people and objects in relation to each other look natural, because the angle of view is similar to the amount you see in front of you that you are aware of, when looking straight ahead, which is about 46 degrees. Some modern compact cameras use a 35mm lens as a standard lens, this is a slightly wider angle lens, with a wider angle of view, and produces a smaller image. There is not much effect on the perspective of objects and it allows the photographer to get more of a subject into the frame.

Move the pointer over the diagram to see a photo taken with this lens.

diagram of a 50mm lens, with a rollover showing a photo taken with a 50mm focal length     

Telephoto lenses

For a 35mm camera, these are lenses with a focal length significantly longer than 50mm. The lens magnifies the image size so that the photographer can take detailed photos from a distance. This is useful when it is impossible to get close to a subject, for example, sports or wildlife photography. Telephoto lenses have a narrow angle of view, that is, not all of a scene will fit into the frame of the photo when using this type of lens, so the photographer must be selective. All telephoto lenses have the effect of reducing depth of field, the longer the focal length, the more noticeable this will be. The photographer must be meticulous about focusing for this reason; it is easy to get the wrong part of an image in focus and the subject you wanted sharp completely out of focus. Perspective tends to be flattened by the magnification of the image, so that relative sizes of distant objects may be difficult to represent. Some extreme telephoto lenses are so powerful they are almost telescopes and can be very heavy and bulky - tripod essential.

Move the pointer over the diagram to see a photo taken with this lens.

diagram of a 50mm lens, with a rollover showing a photo taken with a 50mm focal length     

Wide angle lenses

For a 35mm camera, any lens that has a focal length shorter than 35mm is known as a wide angle lens. It is called this because the angle of view is wide - in some cases, the lens can accommodate more in the frame than the human eye can see when the head is moved from side to side. Extreme wide angle lenses have such a wide angle of view they can almost photograph what is behind them, producing a convex or fish-eye effect. Wide angle lenses decrease image size, so that more can be fitted into the frame of the picture. Distances between objects is emphasised so that perspective seems to be enhanced. Using a wide angle lens for portraiture is not very flattering as noses will look big in relation to faces, if they are nearer to camera, and chins can recede if they are further away. All wide angle lenses tend to have a wide depth of field and it can be difficult to throw a distracting background out of focus because of this. With extreme wide angle lenses it becomes almost unnecessary to focus the lens at all because of the infinite depth of field regardless of camera to subject distance.

Move the pointer over the diagram to see a photo taken with this lens.

diagram of a 200mm lens, with a rollover showing a photo taken with a 200mm focal length