Always remember: The photographer should not expect his exposure meter to know the results he wants. He must be able to use the meter skillfully and interpret its readings carefully in order to get the picture desired. For instance, a meter reading of snow will indicate an "average" exposure that gives detail to the snow. But if you want to represent snow as it more naturally appears, bright and without much detail, the exposure must be increased more than the meter reading. Likewise, a reading of a coal mine tunnel will give an "average" exposure that gives detail to the tunnel. However, if you want the tunnel to be represented in your photograph as it more naturally appears, dark and without much detail, the exposure must be decreased more than the meter reading.

For more exacting exposure guidance for black-and-white photos, photographers can use the Zone System created by well known photographer Ansel Adams. His exposure system requires thorough understanding and extensive practice, but it gives the photographer excellent exposure help, and confidence. Basically, Adams divided the range of subject brightness, or contrast into ten zones, 0 through 9. Zones 0 and 1 represent black (no detail), while Zone 9 represents white (no detail). The other zones represent various shades of gray, with Zone 5 indicating middle gray, the average tone
of a subject as always read by an exposure meter.

This tone (Zone 5-middle gray) can be darkened or lightened to any degree desired by the photographer. Since each change of zone is equivalent to one f/stop, the photographer decides the zone (tone) he wants and adjusts his lens opening (or shutter speed) accordingly. Always decrease exposure to change to a lower zone number (darker tone), and increase exposure to change to a higher zone number (lighter tone).

Obviously, to use this Zone System, the tonal value of each zone must be understood. For example, an exposure meter reading of a persons face will be equal to Zone 5 (middle gray tone), but average skin tones reproduce best as medium light gray, Zone 6. Thus the photographer would adjust his exposure reading by opening up one f/stop. Books are
available on the Adams' Zone System of exposure, and one should be studied for a thorough understanding of its rules
and applications.

While many photographers feel there is no substitute for a hand-held meter, most amateur photographers, and many professionals, rely solely on the exposure meters built in their cameras. Certainly there are advantages and disadvantages to both. The built-in camera meter is quick and less cumbersome since you don’t have another piece of photo gear to carry. However, if the photographer does much of his work using a tripod, a hand held meter gives him the flexibility he needs to make exposure readings away from the camera position. Another plus for a hand held meter is that the full range of exposure possibilities is offered to the photographer. After taking a light reading, he simply looks at the meters calibrated scale and selects the f/stop and shutter speed combination that is best for his purposes.

Regarding exposure meters, I suggest that if you buy a camera with a built in meter and you can make all the types of pictures you want, then the cameras meter is all you need. But if that built-in meter limits the range of photographs you want to make, you had better get a hand-held meter to help you do the job.

Methods of setting exposures on cameras with built-in light meters vary according to the camera design. Of special interest are through the-lens meters used with single lens reflex cameras. Light passing through the lens is measured by an internal meter and indicated for the photographer on a scale within the viewfinder.

While seeking the correct f/stop, the view finder on some SLRs will get darker if the photographer decreases the amount of light coming through it by stopping down the lens. If a small f/stop is needed, say f/11 or f/16, the image the photographer sees will be very dim. He may need to open up to the widest f/stop to focus accurately, and afterward stop down again to get the correct exposure. Setting the exposure on cameras requiring such stop down metering is both time consuming and a nuisance. Fortunately lenses on most modem digital SLR cameras are equipped with automatic apertures which permit what is termed open-aperture or full aperture metering.

With such a lens diaphragm control, the lens stays at its widest opening for accurate focusing and viewing, and then closes down to the selected f/stop when the shutter release is pressed. After exposure, the lens automatically opens up to its widest f/stop again. This automatic stopping down and reopening of the lens is instantaneous.

Some cameras have an automatic aperture override, activated by the depth of field preview device, which allows the photographer to stop down to the selected f/stop without releasing the shutter. This way he can view the scene at the f/stop chosen for exposure and not make a picture.

It is well to remember if you have automatic lens control that when pressing the shutter release to make an exposure, the lens will automatically adjust to the f/stop you’ve chosen. This is mechanical and should occur even if you’re built in exposure meter, which is electrical, is turned off.

On cameras with automatic exposure control, however, the lens may not stop down if the meter is turned off or its batteries are exhausted. Check the camera manual for such warnings.

Automatic Exposure Cameras

The introduction of an electric eye (EE) camera nearly a half century ago sparked interest in automatic exposure control that finally culminated during the last decade or so in a wonderful array of auto-exposure cameras.

They helped sweep aside the past frustrations of getting properly exposed pictures and prompted a worldwide boom in amateur photography. Most of today's popular cameras  utilize automatic exposure systems.

In general, such cameras have photocells which read the light and then set the exposure for the photographer. The simplest cameras take total control of exposure; just set the ISO/ASA dial or lever to indicate the speed of the film you're using and the cameras computer chips do the rest.

As for digital SLR cameras with automatic exposure, depending on the manufacturers design, usually either the f/stop or shutter speed must first be set by the photographer. If the f/stop is preset, the camera is said to have aperture priority (or aperture-preferred) automatic exposure control; when the shutter speed dial is turned to A or Auto position, the shutter speed is automatically set as the shutter release is pressed.

Automatic exposure cameras where the shutter speed is preset are said to have shutter-priority (or shutter preferred) exposure control; when the lens ring is turned to A or EE position, the f/stop is set automatically as the shutter release is pressed.

Some digital SLR cameras feature a programmed mode for automatic exposure control, which sets both the aperture and shutter speed for the photographer. And a few models incorporate automatic multimode exposure control, which permits a choice of aperture priority or shutter priority modes, and sometimes even a programmed mode. Often the multimode models also include a manual mode so you can forgo all automatic exposure controls and set the f/stop and shutter speed yourself.

Automatic exposure cameras have improved greatly since Kodak introduced the first EE camera back in 1938, but they are still not foolproof. More and more are being introduced every year, however, and some photographic experts talk
of total automation some day, even for hard-to-convince professional photographers. While many of the pros would
rather stick by their f/ stops and shutter speeds, new generations of photographers are being raised on automatic exposure cameras and come to depend on them. The trend toward automation will continue; the camera manufacturers will see
to that.

However, with a camera in an automatic exposure mode, an incorrect exposure or no exposure at all will result if the metering system is faulty or turned off. Batteries power the shutter or f/stop mechanisms of such cameras, and they must be operating if the exposure is to be automatically made. Of course, manual operation of f/stops and shutter speeds also is possible with many automatic models. This arrangement, offering a choice between automatic and manual, gives the photographer the flexibility he needs.

For every photographer who understands his exposure system, there are a hundred more who do not, and don't want to. "We just want to shoot," they say, "and not fiddle with camera dials." As long as their results are what they expect them to be, okay. But if a photographer has to sacrifice a good picture because his camera was too automated for him to use creatively, then cameras with automatic exposure control and their future refinements, such as auto focusing, will hinder photographic progress, not help it.

If your camera results in poor automatic exposures, operate it manually until you can have it checked or repaired. Or check yourself you may be operating the camera incorrectly. Study the camera manual again.

Automatic cameras have special problems concerning exposure. As previously explained, after you set the desired f/shop or shutter speed and frame your subject, the exposure meter system automatically sets the appropriate shutter speed or f/stop for the correct exposure. And some cameras are programmed to set both the f/stop and shutter speed automatically. However, the meter can be fooled by the light conditions, and the resulting picture may not be what you had anticipated.

For this reason, the better automatic cameras have an automatic exposure override so you can read and set the exposures manually. On these models there is an exposure control lock so you can preset an f/stop and shutter speed different from the automatic exposure which would result with the scene you’ve framed. After aiming the camera to read an alternate area that you determine will give the proper exposure, slightly depress the shutter release or push a special memory lock lever or button to lock in the f/stop or shutter speed at this camera position. Then reframe your original picture through the viewfinder and fully press the shutter release. This system is convenient once you get used to lt.

A useful exposure override feature on some of the more simple cameras with automatic exposure control is often called a backlight button. With the sun at the back of your subject and shining toward the camera, the cameras metering system may underexpose the photograph. By pressing the backlight button when you take the picture, the camera automatically overexposes the image by about 1.5 f/stops to compensate for the bright light that's adversely affecting the exposure reading.

Versatile digital SLR models have an exposure compensator a dial that is adjusted to automatically underexpose ( - ) or overexpose ( + ) from one half to two f/stops. For example, if you shoot on automatic exposure at the beach or on a ski slope, the light reflecting brightly from the sand or snow can trick your meter into underexposed scenes. To compensate, you would set the exposure compensation dial to +1 or +2 (overexposure) to increase exposure of the image automatically by one or two f/stops. Always remember to reset the compensator to its normal (0) position before you
resume taking pictures under normal light conditions.