Exciting times! Canon, Nikon and Sony all have new full-frame DSLRs that aren't aimed solely at professional or deep-pocketed amateur photographers. Indeed, the Nikon D600 is the first ever full-frame digital SLR to grace Nikon's consumer stable, while the Canon 6D shaves a huge amount off the price of the semi-pro Canon 5D Mark III.

Sony has gone full-frame with its DSLT (Single-Lens Translucent) range, while the Canon 1D X and Nikon D4 build on a rich, fully pro heritage. There's something for everyone, but what's so good about full-frame?

Most consumer class cameras, plus a few professional bodies, use APS-C image sensors. These measure about 25 x 17mm, around the same as a frame of antiquated Advanced Photographic System film with the classic APS-C framing.

Best full-frame DSLR

A full-frame sensor is larger, at 36 x 24mm - the same size as a frame of regular 35mm film.

Historically, physically larger image sensors lent one of two advantages. Firstly, the greater surface area of the sensor could be packed with more pixels, delivering higher-resolution images. This has always been popular for portrait, fashion and landscape photography, because there's the potential for greater detail.

However, an alternative philosophy was to avoid increasing the pixel count, and to make the individual photo sites larger. This gives each pixel a greater light-gathering potential, helping to reduce image noise even in dull conditions.

Quick, quick, slow

Best full-frame DSLR

It's not just about noise. Historically, high-resolution bodies were snapped up by portrait and landscape photographers, while relatively low-res models were more suited to action sports shooters.

For example, the Nikon D3x offers 24.5MP resolution but only a 5fps (frames per second) continuous shooting rate, whereas the Nikon D3s gives 12.1MP resolution but 9fps shooting. Similarly, the Canon EOS 1D Mark III delivers less than half the pixel count of the Canon EOS 1Ds Mark III, but doubles the maximum drive speed.

The new pro Canon EOS-1D X and Nikon D4 hedge their bets, opting for middling pixel counts of 18.1MP and 16.2MP, and maximum drive rates of 11fps and 12fps. The Canon can reach 14fps if you don't mind autofocus and metering being locked straight before the first frame in a sequence.

Best full-frame DSLR

Intriguingly, cameras a step down in price and features from fully pro bodies, such as the Canon EOS 5D Mark III, Nikon D800 and Sony a99, deliver higher image resolution than the really big boys.

The Nikon D800 wins out overall with a monstrous 36.3MP, and the Sony a99 (as well as the cheaper Nikon D600) isn't far behind, at 24.3MP. The Sony still manages a fast drive rate of 8fps, or 10fps in max-speed mode, helped by its fixed, translucent mirror that doesn't need to flip up for each exposure.

In the shallows

Arguably the biggest advantage of full-frame cameras is that they enable a shallower depth of field than APS-C bodies. That's vital for portrait and still-life photographers, who want to blur backgrounds and keep the foreground subject sharp.

Crucially, depth of field is governed primarily by the actual focal length of the lens, rather than its effective focal length after the crop factor has been applied - typically 1.5x or 1.6x for APS-C based cameras.

Best full-frame DSLR

Another bonus is that you can use top-quality lenses, which especially gives Canon and Nikon users a huge choice. Canon has never made any L-series (Luxury) lenses for APS-C format cameras.

Sure, there are benefits of using full-frame sized telephoto lenses on APS-C bodies, to effectively extend their reach. However, the crop factor destroys any wide-angle potential of lenses with short focal lengths.

And if you're going to pay top dollar for quality lenses that create a large enough image circle to cover a full-frame sensor, you might as well use all of it.

Best full-frame DSLR

One final point is that the world often simply looks better through a full-frame camera. The viewfinder image is typically bigger and brighter, enabling a clearer view of what you're shooting. This makes for easier, more precise manual focusing whenever you want to take over control from the camera's autofocus system.

All of the cameras on test have high-quality pentaprism viewfinders, apart from the Sony a99. This camera uses an electronic viewfinder (EVF), which is necessitated by its fixed, translucent mirror design. It has its pros and cons, as you'll see.

None of the cameras here keep things simple. Instead, they're powerful bodies to suit advanced, creative photographers.

Best full-frame DSLR

However, the biggest, most professional cameras go further still, generally sprouting more buttons for direct access to shooting parameters than most people have fingers to press them.

The big boys also have duplicated shutter buttons and command dials for comfortable shooting in portrait orientation.

Now, let's crack on with a closer look at all the cameras in detail, starting with the least expensive at current market prices.