When considering sensor size of digital cameras, the headline figure is the number of megapixels that it can record. There is an implicit assumption that the higher the number of megapixels, the better the end result will be as definition will be greater. In fact, manufacturers have literally made an industry of producing cameras with ever increasing megapixel counts to tempt consumers to upgrade to the next model. Is it really as straightforward as that?

The sensor is the most expensive component to manufacture for a camera. The manufacturing process is not perfect and if all the pixels on the sensor do not function correctly, it cannot be used. The greater the physical size of the sensor, the increased likelihood of dead pixels means that production yields reduce correspondingly, increasing costs.

Sensor size is important as there is a relationship between size and image quality. DSLR sensors are bigger than those in digital compacts, which also means that there is a corresponding difference between the physical sizes of the cameras. The smaller the sensor, the smaller the rest of the camera can be and vice versa.

Consider two sensors, one in a digital compact and the other in a DSLR with both capable of recording 10 megapixels. The greater surface area of the DSLR sensor will mean that it can capture more light, which means that the electronic signal it records has to be boosted less. Since boosting a signal also amplifies any imperfections, the larger sensor will be capable of producing a better quality image.

There is further consideration of this topic in the section on ISO.