Moving up to a full-frame camera brings a modest increase in quality and a big increase in price, so make sure it's worth it.
Most 'amateur' DSLRs and compact system cameras use APS-C size sensors. These are many times larger than the sensors in the average compact camera and deliver the kind of quality needed by professional photographers – or very nearly.
Although many professionals are perfectly happy with the quality they get from an APS-C format camera, it's more likely they'll go for a 'full-frame' camera (the frame is the same size as old 35mm film). These have sensors twice as large again as APS-C and deliver a further improvement in image quality. The differences are not always obvious, but at this level any improvement is useful.
You'll also need a full-frame camera if you want the very highest resolutions currently available – the latest holder of this record is the 50-megapixel Canon EOS 5DS.
Most full-frame cameras are DSLRs. Canon and Nikon make full-frame DSLRs aimed at serious professional users and cheaper full-frame models for advanced amateurs – so the full-frame format is not exclusively for pros.
Sony is following a different path with its full-frame A7-series compact system cameras, like the excellent Alpha A7R III. These look like regular DSLRs but they're more compact and have electronic rather than optical viewfinders. The mirrorless design and full-time live view makes them perfect for shooting video, too, and this is growing in importance as more and more pros find themselves asked to shoot video as well as stills.
Pros: Maximum quality thanks to the full-frame sensor; often designed for tough, daily use; high resolution or high continuous shooting speeds a speciality
Cons: Expensive to buy and that goes for full frame lenses, too; pro models are bulky and heavy
Our pick... Nikon D850
It may be expensive, but if you're looking for the best camera money can buy right now, then Nikon's fabulous D850 DSLR pretty much ticks every box. Packing in a brilliant 45.4MP full-frame sensor, image quality is stunning. But that's just half the story. Thanks to a sophisticated 153-point AF system and 9fps burst shooting speed, the D850 is just a home shooting action and wildlife as it is landscapes and portraits. The Nikon D850 is perhaps the most well-rounded camera we've ever tested.
Read our in-depth Nikon D850 review