October 12 2011
The size of the digital sensor is more important in the performance of a digital camera than the number of megapixels.
When comparing digital cameras photographers often overlook the size of the digital sensor concentrating instead on the number of megapixels.
The physical size of the sensor has a more fundamental impact on the quality of photos. The various ways the size is described is confusing making it difficult to compare sensor sizes.
The sensor size specifications of compact digital cameras are based on old-fashioned type classifications originally used to describe the size of round Vidicon tubes in TV cameras. Compact Digital camera sensors are referred to using old-fashioned imperial fractions of an inch specification that indirectly suggests the size of the sensor.
Although it is written as a number, it is a type, not a measurement. A larger number in the bottom of the fraction is for a smaller sensor. The sensor size graphic above shows the Canon Powershot A470 has a 1/2.3 inch type sensor and is smaller than the Nikon Coolpix P7100’s 1/1.7 inch type sensor.
With a similar number of megapixels in their sensor, digital cameras with different size sensors have different image quality.
The DxOMark test comparison in the table above of three 10 megapixel cameras shows their performance ranks according to sensor size. The new Nikon J1 uses a CX size sensor in the DxOMark tests. The Pentax K10D is an older DSLR with APS-C size sensors yet still outperforms the new cameras with smaller sensors.
Larger sensors allows for bigger individual pixels, and because of their greater surface area large pixels collect more light, and the DxOMark results show they are better performers. In the DxOMark specification comparison the Pixel Pitch is the size of the individual pixels.
Larger pixels are better at collecting light than smaller pixels. One of the key areas where larger pixels excel is in the inherent noise in digital photos, especially those taken in low light conditions. Manufacturers compensate for this with noise reduction as part of the in camera processing. There is a limit to this as too much noise reduction reduces detail, resulting in an unpleasant smeary or plastic look.
This is the same in film photography where larger film sizes result in higher quality photos. The top digital image quality comes from medium format cameras with large sensors from manufacturers such as Hasselblad, Phase One, Mamiya, Pentax and others – not the smaller pro model DSLRs from Nikon and Canon.
While there is a big jump in sensor size of sensors from Point and Shoot digital cameras to DSLRs, there is a much smaller difference between APS-C and Full Frame DSLRs.
The picture quality is very similar and the overall result can depend on where sensor manufacturers introduce the latest technical advances. Currently the APS-C sensor is receiving the latest sensor designs. Cameras such as the Pentax K-5 and Sony SLT A77 are delivering performance equal or better than full frame DSLRs. When they apply this technology to new full frame sensors the results should be amazing, because sensor size does matter.
Photographers comparing only one area of performance of digital cameras do not get the full story of the camera. Sensor size and megapixel count are important, but outside the lab photographers should consider areas such as autofocus, battery life, and ease of operation.