Notes

Just looked up a couple of things on Wikipedia, the font of all wisdom.

Phase-detection autofocus

Main article: Phase detection autofocus

DSLRs typically use a phase detection autofocus system. This method of focus is very fast, and results in less focus "searching", but requires the incorporation of a special sensor into the optical path, so it is usually only used in SLR designs. Digicams that use the main sensor to create a live preview on the LCD or electronic viewfinder must use contrast-detect autofocus instead, which is slower in some implementations.

Pentaprism vs. penta-mirror

Most^{[citation needed]} of the entry level DSLRs use a pentamirror instead of the traditional pentaprism. The pentamirror design is composed mostly of plastic^{[citation needed]} and is lighter and cheaper to produce — however, the image in the viewfinder is usually darker.^{[citation needed]}

Sensor size and image quality

Main article: Image sensor format

Image sensors used in DSLRs come in a range of sizes. The very largest are the ones used in "medium format" cameras, Because of the manufacturing costs of these large sensors the price of these cameras is typically over £13,000.72 as of December 2007.

With the exception of medium format DSLRs, the largest sensors are referred to as "full-frame" and are the same size as 35 mm film  Nikon D800, the Nikon D4, 

Most modern DSLRs use a smaller sensor commonly referred to as APS-C sized, that is, approximately 22 mm × 15 mm,  about 40% of the area of a full-frame sensor. 

Other sensor sizes found in DSLRs include the Four Thirds System sensor at 26% of full frame, 

The sensors used in current DSLRs are much larger than the sensors found in digicam-style cameras, most of which use sensors known as 1/2.5", whose area is only 3% of a full frame sensor. Even high-end digicams such as the Canon PowerShot G9/G10/G11/G12/S100 or the Nikon Coolpix P5000/P6000 use sensors that are approximately 5% and 4% of the area of a full frame sensor, respectively. The current exceptions are the Micro Four Thirds system by Olympus and Panasonic; the Sigma DP1, which uses a Foveon X3 sensor; the Leica X1; and the Canon PowerShot G1 X, which uses a 1.5" (18.7 x 14mm) sensor that is slightly larger than the Four Thirds standard and is 30% of a fullframe sensor. Leica offers an "S-System" DSLR with a 30×45mm array containing 37 million pixels.^[11] This sensor is 56% larger than a full-frame sensor.

There is a connection between sensor size and image quality; in general, a larger sensor provides lower noise and higher sensitivity. There is also a connection between sensor size and depth of field, with the larger sensor resulting in shallower depth of field at a given aperture.