Sigma 18-35mm F1.8 DC HSM A Canon mount lens review: fixed focal length quality in a zoom?By Kevin Carter - Tuesday July 16 2013 Lens Review
With a DxOMark score of 25 points, the lens is a superb performer optically. Ultra-fast lenses don’t usually perform well at full-aperture, let alone high-speed zooms that before this lens arrived usually meant a maximum aperture of f/2.8, but this one bucks that trend.
At 18mm full-aperture sharpness is excellent from corner to corner, though sharpness in the outer field drops slightly through the zoom range to 35mm. For most focal lengths and apertures, though the sharpness differs by 5% or less across the frame.
Distortion, lateral chromatic aberration, even vignetting which appears softly gradated, are all very well corrected for a lens like this. At 1.8TStops, transmission is excellent – this really is an f/1.8 lens and will likely appeal to filmmakers as much as still photographers.