Total Manual Override of Automatic Exposure
Photographers who are comfortable with making exposure calculations and who know what effect they want to achieve prefer manual controls. In this case they set both the shutter speed and aperture based on either the meter (or metering systems) built into the camera or a separate meter, a device that has been used by photographers for more than 100 years.
With the sophisticated technology of digital photography built into the camera, most people will not even consider a hand-held light meter. However, such a meter can be useful when taking product shots or wedding portraits. A hand-held meter allows you to measure the light falling on a subject, for example, not the light reflected from a subject, which is all that the built-in camera meter can do. It also lays out the full range of choices for shutter speed, f-stop, and ISO exposure in a given lighting situation.
Photographers use gray cards, available in camera stores, to help get correct exposures. Place the gray card in front of the subject so that it is in the same light as the subject. Move in close to the card so that all you see in the viewfinder is the gray card. Tip the card so that it appears as bright as possible and has a slight glare. Then tip it again to eliminate the glare and read the camera meter to find the proper settings.
Photography of TVs and computer monitors can be tricky. With a normal shutter speed, a scan line will cut across the screen. You must use a tripod with a slow shutter speed such as 1/8 second or 1/15 second instead. Review your shot with the LCD on your camera. If the scan line still shows, select the next lower shutter speed.