Olympus soon followed with the E-P1, a Micro Four Thirds model with a "flat" design like the pocketable compact digital cameras. These models were followed by Panasonic's GH1, G2, GH2, G10 and G3 (all mini-DSLR style) and GF1, GF2 and GF3 (featuring "flat" designs); and Olympus' E-P2, E-P3, E-PL1, E-PL2, E-PL3 and E-PM1 (all 12.3-megapixel "flat" designs).
In 2010, Samsung introduced the NX10, with a 14.6-megapixel APS-C sensor in a "mini-DSLR" shape, followed by the 14.6-megapixel "flat" NX100, and the new 20.3-megapixel "flat" NX200.
Sony entered the fray that year with the NEX-3 and NEX-5—"flat"-style cameras that were the smallest mirrorless bodies yet, with Sony APS-C sensors. These were followed by the current models, the 16.1-megapixel NEX-C3 and NEX-5N and the 24-megapixel NEX-7, all with Sony APS-C sensors.
Earlier this year, Pentax introduced the Q, a "flat" body that's the smallest interchangeable-lens camera yet—largely because it's built around a 12.4-megapixel compact-camera-size 1/2.3-inch (6.2x4.6mm) sensor.
The most recent company to join the mirrorless interchangeable-lens world is Nikon, with two 10.1-megapixel Nikon 1 models, the V1 and the J1. These cameras feature a new "CX" format: The sensor measures 13.2x8.8mm, about halfway between compact-camera size and Four Thirds System size.
SPEEDToday's DSLRs start up and wake up from sleep mode very quickly, and there's little lag between the moment you fully depress the shutter button to take a shot and the moment the shot is actually taken. And their phase-detection AF systems are very quick, capable of handling the toughest action subjects (in normal mode; in live-view mode, they use contrast-based AF, which is much slower). This hasn't been the case with the compact digital cameras.
But today's mirrorless models also are very quick. They start up and wake up more like DSLRs than like compact cameras, and their contrast-based AF systems are amazingly quick. In fact, current Panasonic mirrorless models offer "the world's fastest level of Light Speed AF with precise Contrast AF"; new Olympus mirrorless cameras provide "the world's fastest autofocus" (claimed to be faster than a top DSLR's phase-detection system); and Nikon's new 1-series mirrorless models offer a hybrid focal-plane phase-detection/contrast AF system that can work at 10 fps.