Sigma 20mm f 1.4 DG HSM A

Designed to compete with the best autofocus lenses from the camera makers, Sigma's Art-series lenses are setting new benchmarks, but as the company expands the range, each model becomes a tough act to follow. Ultra-wides are difficult to produce to a high standard at the best of times and high-speed models are harder still.

Perhaps the biggest problem is retaining affordability. With a list price of £849 it's still quite an investment, but you're getting one of the fastest 20mm lenses available.

The downside to that is it's a big lens with a bulbous front and built-in hood. At close to a kilo, it's heavy and more suited to larger bodies, but that 'steadying' mass and fl.4 aperture should more than make up for that. Like its predecessors it is well made with a mix of plastics and metal, and the extra size means there's plenty of room for a decent-sized focus ring. Like other Art-series lenses, manual focus is stiffer than many other rivals, but that's likely a plus in the long term.

Optically the lens is a great performer. Wide open it has even illumination and, at first sight, has low chromatic aberration, though at times some slight fringing is noticeable in the corners. There's also some curvature of field and astigmatism, which isn't uncommon in lenses like this, but at f4 and above the lens is sharp across the whole frame. It's not perfect - no lens is - but overall it would be a solid choice.