The lab tests show the Canon EF 75-300mm f/4-5.6 III USM and Canon EF 70-300mm f/4-5.6 IS USM have the edge when it comes to sharpness. The scores produced by the Canon lenses are followed closely by the Nikon AF-S DX 55-300mm f/4.5-5.6G ED VR.
When it comes to centre sharpness at the widest focal length, the Canon 70-300mm just has the edge over the Canon 75-300mm, with the Sigma 70-300mm f/4-5.6 APO DG Macro also doing well.
Distortion from all lenses is handled well, with the Sigma 70-300mm f/4-5.6 DG OS showing little sign of distortion wide angles.
We measure sharpness by dividing line width by picture height to give a good impression of performance across the lens.
Here, we measured distortion for each lens at an aperture of f/8. The perfect result would be 0 per cent.
Shooting at f/8, we measured fringing in pixels at the centre point of each lens. The perfect result in this test would be 0 per cent.
Despite the sharpness performance of the Canon 70-300mm, it suffered from the greatest degree of distortion at 70mm, but this was easily corrected when processing.
Fringing is most noticeable in images taken with the Sony 75-300mm f/4.5-5.6 and the Canon 75-300mm at 300mm, while the least fringing was seen in the Sigma 70-300mm f/4-5.6 DG OS.
The Canon 70-300mm f/4-5.6 IS USM came out top in the lab tests, despite issues with fringing at 300mm.