Most professional photographers choose a full frame DSLR over any other camera type. They're larger, heavier and certainly more expensive than APS-C format DSLRs, but for full frame fans they're worth it.
Full frame DSLRs aren't just for pros, though. Canon and Nikon make lower cost DSLRs for enthusiasts and experts who want the best possible quality but don't need (or can't afford) full-on professional cameras.
Full frame sensors are twice the size (in area) of the APS-C sensors used in mid-range and entry-level DSLRs, and this gives them a number of advantages:
For a given resolution, a full-frame sensor will have larger photosites (pixels) so you'll get better quality at higher ISOs.
But makers can also use the larger area for higher resolutions without compromising low-light performance – the Nikon D810 has 36 million pixels and the Canon 5DS will have 50 million.
The larger sensor means you use longer focal lengths, and this gives shallower depth of field and more pronounced defocus effects – perfect for portraits, sport shots and any scene where you want to tone down a cluttered background.
All this costs money, however, and not just for the camera itself – you may also need to invest in new lenses, even if you have some already. You can't use Canon EF-S lenses on its full-frame cameras, for example, and while you can use Nikon DX lenses on a Nikon FX full frame camera, they'll only work in 'DX crop' mode, which negates the advantage of the bigger sensor.
If you're not sure, you might want to take a look at some full-frame alternatives instead:
But if you're sure full format is the way you want to go, here are a few features to look out for:
Megapixels: Most full-frame DSLRs have around 20 million pixels – about the same as APS-C DSLRs, interestingly, and chosen as a compromise between resolution and overall image quality. At the top end, though, manufacturers tend to choose speed or resolution – the Nikon D4s has just 16 million pixels but shoots at 11fps, while the D810 has 36 megapixels and shoots at 5fps.
Construction: Cheaper full frame DSLRs are built to a high standard, but the pro models are built around a metal chassis and designed to survive heavy professional use over a long period of time. The D4s has a rated shutter life of 400,000 shots.
Continuous shooting speed: If you need to capture sports and action, and to shoot in really low light, you need the Canon EOS-1D X or Nikon D4s, end of story.
AF system: The cheapest cameras in this group use AF systems from the amateur DSLR market – they're perfectly adequate for relatively static or slow-moving subjects, but for action photography you're better off with the Nikon 51-point AF or Canon's 61-point AF systems, found in the more advanced models
Lens choice: When you invest in a full frame camera you're also investing in the lens and accessory system behind it. Canon and Nikon are in the lead here, and while Sony is ramping up its full frame system, most of the effort is going into its A7 compact system camera range. There are some good lenses for the Sony Alpha A99, but its future is unclear.
Best full-frame DSLR: Nikon D810
Price: about £2349/US$2997, body only | Megapixels: 36.3 | Autofocus: 51-point AF, 15 cross-type | Screen type: 3-2 inch, 1,229,000 dots | Maximum continuous shooting speed: 5fps | Maximum video resolution: 1080p
The Nikon D800's 36.3Mp sensor caused a big stir when it was released in 2012, offering the highest resolution of any Nikon SLR to date. While this enables superbly detailed images, you'll need to make sure your focusing skills (and lenses) can keep up, as any lack of sharpness is more obvious.
Nikon has since replaced the D800 with the D810, which keeps the same resolution but removes the anti-aliasing effect from the filter in front of the sensor (the earlier D800E offered a reduction in anti-aliasing rather than full removal).
The D810 brings a number of improvements over the D800, including a higher resolution display, faster continuous shooting (5fps vs 4fps), 33% longer battery life and Picture Control 2.0 image effects, which now include a Clarity micro-contrast adjustment and a Flat mode for maximum dynamic range – especially useful for video.
The D810 has a 51 point AF system compared to the 61 point system in the Canon 5D Mark III, but it copes admirably with tricky focussing situations. Indeed, both the AF and metering systems are identical to those in the Nikon D4s, but at a much lower price. Considering its massive resolution and advanced features, the D810 is reasonably light and the pop-up flash is a useful bonus.