The best Photo shot, getting Cameras the Exposure Right part 1

Choosing the best exposure for a picture is just as important as getting the image sharp. A beautiful holiday picture on the beach is spoiled if you cannot see details of the people in the photographs—they may be too light or dark.

A correctly exposed negative or slide will have a full range of tones from deep shadows to bright highlights. Under-expose your photograph and the darker parts of the picture will contain little detail; over-expose, and the bright parts will appear all washed out and lacking in detail.

Guessing the exposure (based on the film manufacturer’s guide sheet in every film pack) may be successful on a reasonably bright day when there are no deep shadows or patches of very strong sunlight. But the more extreme the lighting conditions become, the more difficult it is to guess accurately.

Camera Meter

An exposure meter measures the brightness of the subject and, based on the speed of the film you are using, gives you a guide to the f number and shutter speed to use. Most 35mm cameras, especially SLRs, and even some 110 cameras, now have built-in exposure meters. Some work automatically and set the camera’s controls for you, but with others you have to adjust either the shutter speed or the aperture manually. Hand-held exposure meters are still used too, mainly for special situations like low light or night photography, and for incident light readings.

Both hand-held and built-in exposure meters contain a photo-electric cell which measures the amount of light falling on it. There are three types of cell.

Selenium cell: too large for most built-in meters, a selenium cell powers itself. It needs no batteries. Any light which reaches the cell generates a small electric current which is measured by a galvanometer needle along a scale. Used mainly in handheld meters, this type doesn’t respond well in very low light.

The CdS cell: the development of a tiny, sensitive cell using cadmium sulphide made built-in meters possible for the vast majority of 35mm cameras. It can give readings even in moonlight, but takes a little time to settle down if you move quickly from bright sunshine to dark shade.

Silicon cell: the newest meters use a miniature silicon cell. This is very accurate and adjusts quickly to changing light conditions. It can cope with any contrast, from the brightest sun to night-time. Miniaturization has made this cell so small that, even with an amplifier and batteries, it can be fitted into a 110 camera.

Through the Camera lens metering

The majority of SLR cameras have built-in meters which measure the light entering the lens. The meter often has the same angle of view as the lens on the camera so measures light over a wider area for a wide angle lens, and over a narrower area for a telephoto. Some TTL meters take an average reading from the total amount of light entering the lens, not differentiating between bright areas of sky and the darker land. Others, which are more accurate, also measure the light as a central spot (perhaps one-fifth of the total picture area). The best alternative is probably to use a third systemcentre-weighted. This gives preference to the light reading at the centre of the picture using one cell, but co-ordinates with a second cell which takes the rest of the frame area into account.

Exposure information collected by the metering system is usually displayed in the viewfinder in one of two ways: either by a needle which moves between two markers or by LEDs (small bright lights) which are colour coded for correct over- or underexposure. These lights are less easily affected by rough handling than the older, needle systems, but use up battery power much faster.

Camera Automatic metering

An increasing number of SLR and viewfinder cameras with meters are semi or fully automatic. The latter select the correct exposure combination without the photographer’s help. But there are two types of semi-automatic cameras; those which select a shutter speed to match the f number chosen by the photographer (aperture priority) and those which select the right aperture to suit a manually set shutter speed (shutter priority).

Aperture priority suits still subjects, landscapes and pictures in which depth of field is important.

Shutter priorityhas the advantage when photographing moving subjects, because you choose the shutter speed. Stopping movement is more important than depth of field.

A few of the more expensive cameras, like the Canon A-1, have a choice of priorities, including fully automatic exposure control which requires no manual setting of aperture or shutter speed. You can move from one to the other or take full manual control at the flick of a lever.

Integral Camera exposure meters

Some viewfinder cameras also have integral exposure meters. These do not meter through the lens, but use a cell mounted either next to the viewfinder window or surrounding the lens (Olympus Trip 35). They are usually coupled to the aperture/shutter mechanism in the same way as SLR cameras, although most are fully automatic. With other models, you simply align a needle or see a light that indicates the correct exposure.

Possibly related posts: (automatically generated)
The best Photo shot, getting Cameras the Exposure Right part 1

• How to use your Camera to shot good Pictures/Photo (Infra-red index; Mirror lock and Shutter lock)
• How to use your Camera to shot good Pictures/Photo (Depth of field preview)
• How to use your Camera to shot good Pictures/Photo (Multiple exposures; Cable release socket; Delayed action; Flash synchronization)
• How to use your Camera to shot good Pictures/Photo (Exposure memory; Exposure compensation)
• How to use your Camera to shot good Pictures/Photo (Film plane index; Battery check; Rearsight features; Film memo holder)
• Camera Exposure metering systems
• The best Photo shot, getting Cameras the Exposure Right part 2
• Taking Sharp Pictures
• Cameras Focusing Screens and Viewfinders
• Digital Electronic Cameras, basic knowledge and care the Lens