Photography rules (5)

Metering Modes
The camera’s exposure sensor, known as an exposure meter, does the majority of the work when figuring out how to shoot a picture. It decides how much light is needed to adequately expose your picture. So it should come as no surprise to learn that cameras distinguish themselves by the kind of meter they use. Some meters are better than others at metering a scene and applying the right exposure.

Center-Weighted Meters
This meter measures the light throughout the image, but applies more weight, or importance, to the central part of the scene in the viewfinder. The assumption, usually a good one, is that you are most interested in the stuff in the front of the picture, so the camera tries to get that part of the scene exposed properly. Most digital cameras rely on this for ordinary picture taking.

Matrix Meters
The matrix meter is famous for its ability to properly expose tricky scenes by balancing the lighting needs of five or more discrete regions within a picture. Instead of concentrating primarily on the middle, matrix meters gauge the light in many parts of the scene at once. If your camera has a matrix meter mode, you should use it most of the time.

Spot Meters
The last major kind of light meter is called a spot. The spot meter is never the only kind of meter in a camera; instead, it’s an option that you can switch to if the center-weighted or matrix meter fails you. The spot meter measures light exclusively in the center one percent of the screen, ignoring the rest of the frame completely. That can come in handy on occasion, but a meter that only measured the light in the central one percent of the frame would typically take very poor pictures, either highly under- or overexposed depending upon the situation.
So when should you use the spot meter? Any time you are trying to photograph a scene in which a small subject must be exposed properly for the picture to work and its lighting is different enough from the rest of the scene that you’re worried it won’t come out right otherwise.
Imagine, for instance, that you are trying to photograph someone who is standing in front of a brightly lit window. If you let the camera decide the exposure, the bright light from the window will radically underexpose the subject. So switch on the spot meter and expose the picture based on the subject. Yes, the window light will be overexposed, but that’s okay, the important part of  the picture is the person.
Varying the metering mode, especially the spot meter, is best used in conjunction with the exposure lock.

Using Exposure Lock
Exposure lock is almost always achieved by applying slight pressure to the shutter release, not enough to activate the shutter and take the picture, but enough that you feel the button move and the camera itself respond.
The magic of exposure lock is that as long as you continue applying light pressure to the shutter release, the camera will use that “locked-in” exposure information regardless of where you later point the camera. You can lock in exposure information for the sky and then point the camera at your feet and snap the shutter release all the way. You’ll take a picture of your feet using the sky’s exposure data. You probably wouldn’t want to do that since the result will be totally underexposed, but it gives you an idea of the potential.
Exposure lock is a great tool for telling the camera that you’d like to take a picture with the exposure data from one specific part of the scene.

When to Take Control
You may often be perfectly satisfied with the results you can get from the automatic exposure controls in your camera. But there will be times when you can do better on your own.

Very Bright Sunlight
Very bright sun can overwhelm your camera, especially if the scene is filled with brightly colored clothing, reflective surfaces, or other tricky subjects. You can reduce the exposure for better effects. Underexpose the scene by EV –1 for starters, and see if that helps.

Backlit Subjects
If you are taking a picture of someone or something and the sun is behind the subject, you’re usually in trouble—the bright background will cause the camera to underexpose the scene. That means the subject itself will look like it’s in shadow. The best way to shoot an outdoor portrait is to put the sun over your shoulder. Nonetheless, if you find the sun behind your subject, overexpose the scene, such as with an EV +1.

Low Light
In low light, such as at night, indoors, or under thick cloud cover, you can often get better results by overexposing the scene slightly, such as with an EV +1. Vary the EV level depending on how dark the scene actually is.

Using Exposure Compensation
Most digital cameras come equipped with an exposure compensation control, usually referred to as the EV adjustment. The EV control allows you to lock in and use the camera’s recommended automatic exposure setting, but then adjust that value up or down based on factors that you’re aware of but the camera may not be smart enough to see. Each Exposure Value (EV) corresponds to changing the exposure by one stop, such as going from 1/60 to 1/30 (this is a change of +1 EV since it doubles the exposure) or 1/15 to 1/30 (this is –1 EV since it reduces the exposure by half). 

to be continued