Click to explore the sizes of image sensors.

The image sensor in a camera has two important and related physical characteristics— it's size and aspect ratio.

Sensor Size

Image sensors come in a variety of sizes with the smallest ones used in point and shoot cameras and the largest in professional SLRs. Consumer SLRs often use sensors having the same size as a frame of APS film. Professional cameras occasionally use sensors the same size as a frame of 35mm film—called fullframe sensors. Larger image sensors have larger photosites that capture more light with less noise. The result is pictures that are clearer, brighter, and sharper. Because the size of photosites is so important, a large 6 Megapixel sensor will often take better pictures than a smaller 8 Megapixel sensor. Not only is noise a problem but smaller sensors also require better, more expensive lenses, especially for wide-angle coverage. Here are some typical sensor sizes:

Aspect Ratios

Image sensors come in a variety of aspect ratios— the ratio of image height to width. The ratio of a square is 1:1 (equal width and height) and that of 35mm film is 1.5:1 (1� times wider than it is high). Most image sensors fall in between these extremes. The aspect ratio of a sensor is important because it determines the shape and proportions of the photographs you create. When an image has a different aspect ratio that the device it's displayed or printed on, it has to be cropped or resized to fit. Your choice is to loose part of the image or waste part of the paper. To imagine this better, try fitting a square image on a rectangular piece of paper. To calculate the aspect ratio of any camera, divide the largest number in its resolution by the smallest number. For example, if a sensor has a resolution of 2816 x 2112, divide 2816 by 2112. In this case the aspect ratio is 1.33, slightly squarer than 35mm film but the same as computer displays.