Studio Tests - APS-C format
The Canon 50mm F1.4 distinctly struggles on APS-C at wider apertures (where it is outclassed by the Sigma 50mm F1.4 EX DG HSM), but improves rapidly on stopping down, performing very well at apertures of F2.8 and smaller. As usual it benefits from the 'sweet spot' advantages of low distortion and minimal vignetting which are common to shooting full-frame lenses on APS-C.
|Sharpness||The Canon 50/1.4 is distinctly soft wide open on APS-C, especially towards the corners. However central sharpness increases rapidly on stopping down, with the corners slowly but surely catching up. Optimum results are obtained between F5.6 and F8, at which point the lens is very sharp right across the frame; at smaller apertures, diffraction progessively reduces sharpness, with anything beyond F16 best avoided unless extreme depth of field is critical.|
|Chromatic Aberration||Lateral chromatic aberration is essentially a non-issue (a fundamental characteristic of the traditional symmetric design of 50mm lenses). However the non-zero CA figures towards the centre at wide apertures betray a more problematic issue, high levels of mainly blue 'colour blur' due to axial chromatic aberration, which disappear on stopping down to F2.8.|
|Falloff||We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the centre. As usual for a full-frame lens used on APS-C, there's really nothing to worry about here (although the measured vignetting pattern is noticeably asymmetric, presumably due to the shape of the 450D's mirror box).|
|Distortion||Distortion is very low at just 0.5% barrel, a figure too low to have any significant impact in real-world use.|
Specific image quality issuesAs always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests.
Softness wide open
Not unusually for a full-frame optic used on the resolution-hungry APS-C format, this lens distinctly fails to shine at wide apertures. In this regard it's worth noting that depth of field is so shallow at F1.4 that real-world results are mainly dependant upon focus accuracy, and this lens will tax the abilities of any focusing system, either auto or manual (not to mention the fact that the slightest relative movement between photographer and subject will result in a misfocused image). However even at its best, this lens never really looks properly sharp wide open. The situation is exacerbated by the high levels of blue channel 'colour blur' revealed in our studio tests, which contribute significantly to the lens's characteristic 'dreamy' signature at F1.4-F2.
For brick wall connoisseurs, here's a comparison between the lens shot at F1.4 and F4, using Canon's most demanding APS-C camera to date, the 15Mp EOS 50D. This shows very clearly the low contrast and lack of detail at F1.4; it also shows that the lens is fully capable of matching the 50D's sensor at F4 in the centre of the frame, but still struggles slightly at the corners.
|Canon EOS 50D||Canon EOS 50D|
|100% crop, centre of frame||100% crop, centre of frame|
|100% crop, top left corner||100% crop, top left corner|
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