Most people don't realize that not all digital cameras are created equal in terms of their format, in other words the size and shape of the silicon sensor used to form the image. The size and shape of the sensors do affect the final image and often in ways that the average user is not fully aware of. Here is an examination of what's currently available and how it affects the photographer.
A comparison of the formats
On the left you will see a chart that I made comparing the various formats most popular in digital cameras. Only four of these are widely used in interchangeable lens cameras (ILCs) by the leading camera brands: Canon, Nikon, Olympus, Panasonic, Pentax, and Sony. Click on the image to enlarge it.
Full Frame (35mm) digital cameras - 36x24mm
Known as "full frame" cameras to distinguish them from the smaller sensor "crop sensor" cameras that use the same lenses and have the same 35mm Single Lens Reflex (SLR) design, full frame cameras have a sensor the same size as 35mm film - 24x36mm.
Crop Sensor "APS-C" digital cameras - 16x24mm
The first digital Single Lens Reflex (SLR) cameras had electronic sensors custom built into the bodies of 35mm film cameras, the cameras of choice for most photographers due to their high quality, small size, ease of use, and wide selection of lenses. The sensors were small and low resolution by today's standards, with the roughly 16x24mm size now called "APS-C" quickly becoming the most common size.
Crop Sensor "4/3" digital cameras - 13x17mm
There are only two manufacturers currently making cameras in the 4/3 format: Olympus and Panasonic. But what cameras they are making! Both of them have quite a following, with Panasonic seeming to target the video crowd and Olympus aiming squarely for the still shooters. Since the lens mounts are the same on both cameras, each manufacturers lenses will work on the other's cameras.
1 inch sensor cameras - 9.6x13mm
Nikon is the only company offering an interchangeable lens camera with a one inch sensor, but Sony, Panasonic and Canon offer fixed-lens cameras with the same size sensor, all capable of giving excellent quality images.