Photographie and Sound health

Digital SLRs use light-sensitive electronics to measure the light passing through the lens. In early days of non-digital SLRs, that capability was considered something of a miracle in itself because cameras of that era frequently captured exposure information through clumsy photocells mounted on the outside of the camera body. The alternative was to use a handheld meter. Such systems were relatively low in sensitivity, and you had to be incredibly lucky for the light captured by the meter to have some correspondence with the illumination that actually reached the film. Of course, if you used a filter or other add-on, all bets were off. Photographers were delighted when cameras were introduced that actually measured light destined for the film itself. Digital SLRs use much more refined methods of metering light, compared to the earliest through-the-lens models, which captured an amorphous blob of light without much regard to where it originated in the image. Modern metering systems can be divided into several categories.

Center weighting: While early cameras had a form of averaging metering, in which light from all portions of the viewfinder was captured, in truth they tended to emphasize the center portion of the frame. This bug was turned into a feature and center-weighted averaging was born. Most of the exposure information is derived from the middle of the frame.

Multipoint metering: Exposure information is collected from many different positions in the frame, and then used to calculate the settings using one of several calculation routines. The picture below shows a typical multi point arrangement.