Mount: Canon | Construction: 13 elements in 10 groups, 8 diaphragm blades | Closest focus distance: 25cm | Filter thread: 77mm | Autofocus: ring-type ultrasonic | Dimensions: 80 x 87mm, 650g
This is the mark II edition of this lens and isn't just a minor tweak but represents a complete redesign. It boasts an extra two elements, taking the total number from 11 to 13, and its more rounded aperture is based on eight rather than seven diaphragm blades.
As one of Canon's L-series (Luxury) lenses, it has professional-grade build quality and comes complete with weather-seals, although the latter isn't true of all L-series lenses.
Like other wide-aperture wideangle prime lenses, the Canon 24mm f/1.4 is pricey, but it does have a particularly strong build, based on a metal rather than plastic barrel. There's a floating and fully internal focus system, powered by a ring-type ultrasonic autofocus mechanism.
Up-market glass includes two aspherical elements to guard against spherical aberrations (a common issue with wide-aperture lenses) and two Super UD (Ultra-low Dispersion) elements to correct lateral chromatic aberrations. The lens also features Canon's 'Subwavelength Structure Coating' to reduce internal reflections and cut ghosting and flare.
While the availability of a wide f/1.4 aperture is great to have, the image quality is unimpressive at this setting. Vignetting (darkened image corners) is very pronounced, and there's a distinct lack of sharpness towards the edges and corners of the frame. Our review sample also suffered from a front-focus issue during autofocusing, although this was effectively bypassed in Live View mode. For best image quality with this lens, it's best to stick to apertures of between f/4 and f/8.
For our lab tests we shoot test charts under controlled lighting conditions. The results are processed using the industry-renowned Imatest Master software suite, so that we can measure optical performance in terms of sharpness, chromatic aberration and distortion.
Sharpness: The sharpness chart provides an indication of lens performance across the focal range (for zoom lenses) and at different lens apertures.
Despite being one of the more expensive wideangle prime lenses, the Canon's sharpness is unimpressive, especially away from the centre of the frame.
Fringing: We test colour fringing (chromatic aberration) at several lens apertures. Lower scores are better.
Distortion: -0.43 (barrel distortion)
Barrel distortion is well controlled with this lens. Values closest to zero are best, negative values indicate barrel distortion and positive values indicate pincushion distortion. Distortion is unaffected by lens aperture but does change with the zoom setting.
This lens's sharpness is unimpressive at the centre and disappointing towards the edges and corners. We'd expect better at this price.