Full Frame Cameras
Photography the way God intended
Most digital SLRs have 'crop' sensors, meaning their size is smaller than the traditional or 'full frame' area common in the 35mm film era. Full frame cameras provide a little more than 2.5 times the area of crop sensors (commonly referred to as APS-C). This huge size increase lets camera manufacturers include more pixels for higher resolution or increase the size of the pixels for superior dynamic range and low-light capability. More commonly, manufacturers will increase both the resolution and the pixel size.
There are several downsides to full frame cameras. The first and most significant is price. Full frame cameras are frequently several thousand dollars more expensive than their APS-C brethren. The cost of entry into the full frame world is starting to decline, though. Nikon's more affordable D600 and Canon's new 6D both drop the point of entry significantly, but do so with some compromises. Sony recently rocked the full frame world with their full frame mirrorless cameras, the Sony A7 and A7R, which match the $2,000 entry point of the D600 and 6D but do so in a much smaller body.
It's worth mentioning too, that the price premium isn't reserved to the cameras themselves. Full frame lenses are much more expensive than those designed specifically for APS-C cameras. The reason for this price difference is that larger sensor area requires the use of much larger optical elements. Since these elements are solid hunks of glass, you'll also be carrying a lot more weight with you. That's the second major downside to full frame - the larger and heavier gear you have to carry around to enjoy the full-frame benefits.