Digital Camera Master

What makes a camera a digital SLR, anyway? And how is it different than a point-and-shoot camera?

If you’re familiar with film cameras, then you know that SLR stands for single lens reflex, a system which uses mirrors and lenses to capture an image. When a photographer looks through a lens on an SLR camera, the image he sees enters the camera, hits a mirror, and then bounces through a prism onto a focusing screen. Just before the shutter is snapped, the mirror swings out of the way to expose the image onto a piece of film. With an SLR, the photographer sees exactly what the camera sees.

Digital SLRs work in the same way, although the image is captured by a digital image sensor instead of film. Like film, the sensor in your digital camera is sensitive to light; it records the amount of light that hits its surface when the shutter is opened. Color is achieved by a filter that’s placed over each pixel on the sensor. In a digital camera, the union of pixel and its filter is called a photosite. Figure 1 shows how a filter grid looks.

Figure 1. A digital sensor is composed of millions of photosites, also called pixels, which collect light during an exposure. Circuitry then converts this light into image data that becomes a digital photo at the end of the process.

Point-and-shoot digital cameras, also called digicams, are simpler in design than dSLRs, and their smaller sensors and photosites put limitations on image quality.The most obvious distinction between the two camera types is that lenses on dSLRs are interchangeable, just like with their film cousins, whereas digicams sport a single lens that’s affixed to the body. The ability to exchange lenses depending on the situation or artistic intent makes dSLR cameras much more versatile than digicams.