Lenses

Lenses:


WIDE ANGLE LENSES

(ie 35mm, 28mm, 24mm and wider) Apart from "getting more in a picture" than a "standard" lens, appear to emphasize/exaggerate any subject in the foreground, making the background appear smaller and more distant. The shorter the focal length the greater the effect.

TELEPOHTO LENSES

(ie 85mm, 135mm, 200mm, 400mm) Have a narrower angle of view than "standard" lenses, enabling a close-up to be taken of more distant objects. They also appear to "pull the background", giving the impression of compressing the distance between a subject and the background. The longer the focal length, the greater the effect. Head and shoulder portraits are often taken with lenses in the 85 to 135 mm range.

ZOOM LENSES

Enable the user to alter the focal length of the lens, the angle of view for the close-ups, to isolate a subject, or to improve composition. These lenses are generally "slower" than prime (fixed focal length) lenses, often having a maximum aperture of f4.

With many zoom lenses the "effective" aperture changes as the focal length increases. F8 at the wide-angle end becomes F11 at the telephoto end due to the lens extension; through the aperture setting on the lens barrel does not change. There is no problem with continuous light as the exposure meter will take this into account and still indicate when your aperture/shutter speed settings will give correct exposure. When photographing by electronic flash this change in effective aperture may need to be taken into account to avoid the possibility of under exposure. Zoom lenses set at F8, but on telephoto setting giving an effective aperture of F11, use flash at an F11 setting.

MACRO LENSES

Usually made of two focal lengths, 50 mm(standard) and 100mm. They are especially designed to be used for extreme close-ups, but can also be used of "general photography".

TELECONVERTERS

Are "supplementary lenses" used between the camera and a "normal" lens. They effectively double the focal length of a lens. (ie: a 135mm lens becomes a 270mm lens).


SUPPLEMENTARY CLOSE UP LENSES

Are available in +1, +2, +3 and +4 dioptres (just like close up reading glasses) and can be screwed into the filter thread on the front of ht lens, enabling it to be focused at a much closer distance than normally possible. These supplementary lenses tend to make the field of view slightly wider than normal.

CATADIOPTRIC LENS

Uses mirrors and elements to fold the light path to fit long focal lenses into short barrels. They are often referred to as "Mirror Lenses" and usually have a fixed aperture (often F5.6, F8 or F11). Out of focus highlights are reproduced as small circles or "donuts".

PERSPECTIVE CONTROL LENSES

Have a movable front element and are often used in architectural photography. Tall buildings can be photographed from ground level without distortion or the need to tilt the camera upwards.

DEPTH OF FIELD

The aperture and the distance at which a lens is focused determine the depth of field (area in sharp focus) in a picture. This has one third in front and two thirds behind the point at which the lens is focused. The wider the angle (the shorter the focal length) of a lens, the greater the depth of field (ie. 28mm greater than 50mm). The depth of field changes as the camera to subject distance is altered. The closer the lens is to the subject, the shallower the depth of field becomes. Depth of field increases as any lens is stopped down, from F4 ti F8, F16, F22 etc, through the long telephoto lenses have very shallow area in sharp focus, even at F22. The whole scene, from foreground to infinity, can often be rendered sharply by using a small aperture (F16 etc), or a large aperture can be used to selectively focus on a subject, isolating it from a blurred background, especially with longer than normal focal length lenses which have a shallow depth of field.