When you're shopping for a camera, you have a million specs and features to consider. Can you guess which aspect consumers consider most important?

The color of the body. The camera buyer for a national electronics chain told me that.

What you should care most about is the flat, rectangular light sensor inside the "film." In general, the bigger the sensor, the happier you'll be with the results and the more you'll pay.

At the low end, snapshot cameras with tiny sensors (0.4 inches diagonal) cost $150 but give you blurry, grainy low-light shots. At the high end, those professional, big, black SLR cameras cost $2,000 to $6,000 but come with full-frame sensors, as big as an old piece of 35 mm film (1.7 inches). They deliver unparalleled low-light quality, richness of color, detail and soft-focused backgrounds.

All of this explains why Sony's 2013 camera/camcorder lineup is so startling. The company has put full-frame sensors into three new cameras, at prices and body sizes that nobody has attained.

For example, there's the A99, which Sony says is the world's smallest and lightest full-frame SLR. It's meant to compete with professional cameras like the Canon 5D Mark III ($3,200) and Nikon D800 ($3,000) -- for $2,800. (These prices are for the bodies only.)

The A99 is sort of homely, but it has a long list of distinguishing features: fast, continuous focusing, even while filming or shooting something running at you; two memory-card slots; built-in GPS function that stamps every photo with your location; 1080p, 60-frames-a-second high-definition video; microphone and headphone jacks; and an electronic viewfinder whose video shows you the results of your adjustments in real time.

Then there's the VG900, Sony's first full-frame camcorder. It costs $3,300 -- about $10,000 less than any other full-frame camcorder, Sony says. And its sensor is about 45 times as big as a standard camcorder's sensor.A big sensor gives you amazing low-light video, gorgeous blurry backgrounds, greater dynamic range and better color.

The most astonishing new full-frame Sony, though, is the RX1. It's the world's first compact full-frame camera.

The RX1 is easily coat-pocketable, but yes, there's a full-frame sensor in there, and the photos it delivers are breathtaking.

You'll pay a crazy price for this achievement: $2,800.

That's not the only price you'll pay for this amazing act of miniaturization. This camera doesn't zoom, apart from a 2x digital, fake zoom. And its lens is permanently attached.

So who on earth would pay $2,800 for a nonzooming camera?

The Sony RX1 takes certain photos better than any other pocketable camera in the world -- low-light shots, for example.

Clearly, this camera is intended for professionals or nearly pros.

You may scoff at its nonzooming lens, its slowish focusing and its nosebleed price, and that's fine; in many ways, the RX1 is a proof of concept, a bold experiment, an effort to achieve what's always been thought unattainable.

It paves the way for other cameras that you may want to buy, cameras that embrace the philosophy of big sensors in small bodies.