Studio Tests - APS-C format
The Sony 50mm F1.4 performs extremely well on APS-C for a conventional (all-spherical) design, outclassing the equivalent lenses from Canon, Nikon and Pentax. It shows unusually high central sharpness even wide open, and as usual benefits from the 'sweet spot' advantages of low distortion and minimal vignetting which are common to using full-frame lenses on APS-C. Compared to the Sigma 50mm F1.4 EX DG HSM, the Sony shows higher central sharpness (although with noticeable halation) but less consistency across the frame at wide apertures. Compared to the parent Minolta 50mm 1.4 RS, the Sony lens shows increased sharpness at all settings, but at the expense of measurably higher chromatic aberration; all other characteristics are virtually identical.
|Sharpness||Central sharpness is high even wide open, although the corners are rather soft. However these improve rapidly on stopping down, and sharpness becomes excellent right across the frame at just F2.2. Optimum performance is achieved between F3.3 and F8, with the lens delivering excellent results right across the frame at these apertures. As usual diffraction takes its toll at smaller apertures, softening the image significantly.|
|Chromatic Aberration||Lateral chromatic aberration is measurable, but in real-world terms essentially a non-issue (a characteristic of the traditional symmetric design of 50mm lenses). The non-zero CA figures towards the center at wide apertures betray a more problematic issue, high levels of 'colour blur' due to axial chromatic aberration; however this disappears on stopping down to just F2.0.|
|Falloff||We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the center. As usual for a full-frame lens used on APS-C, there's really nothing to worry about here.|
|Distortion||Distortion is extremely low at just 0.3% 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.
Depth of field is extremely shallow at F1.4, and real-world results therefore become highly dependant upon focus accuracy. 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). Sometimes individual samples of a lens can show consistent misfocusing problems, with the region of critical focus slightly ahead of, or behind the desired point - errors which are known as front- and back-focus respectively.
Our test sample of the Sony 50mm F1.4 showed a clear back-focusing problem, and neither of the APS-C bodies we tested it on (Alpha 700 and Alpha 350) were able to focus it accurately for use at wide apertures. This gave shots which, while fine for full-screen viewing or relatively small prints (5"x7"), were consistently misfocused when viewed at 100% - which would translate to visible issues on larger prints.
The sample below is illustrative of this issue - focus was confirmed by the camera on the eye, but even at F2 this is visibly soft, and sharpest focus is in the region of the ear. One or two shots like this we'd happily ascribe to user error, but the consistency of the issue indicated a lens problem instead, which was confirmed by more formal 'ruler tests' in controlled studio conditions.
|F2, Sony Alpha 700||100% crops|
We were able to mitigate this problem on the A900 using an AF microadjust of -7, but on older bodies we'd consider this performance unacceptable and get the lens either repaired or replaced.
Soft corners wide open
Not unusually for a full-frame optic used on the resolution-hungry APS-C format, this lens has its problems at wide apertures; however the unusually high central sharpness mean that these are mostly confined to the edges and corners of the field. This in principle makes the lens capable of shooting normal three-dimensional subjects placed towards the center of the frame quite convincingly even wide open; in such cases the peripheries of the frame will likely be well outside of the depth of field, and corner softness issues irrelevant.
To illustrate corner softness issues on APS-C for brick wall connoisseurs, we used the Alpha 900 in crop mode (to get accurate focus at F1.4). This results in a 10.7Mp APS-C format image - only slightly behind the 12 Mp Alpha 700 in captured detail. Images are compared at F1.4 and F2.8 - the central 100% crop shows a high level of detail is resolved at 100%, but at low contrast. In contrast the corners show distinct softness at F1.4, but improve dramatically at F2.8.
|Sony A900, APS-C size capture||Sony A900, APS-C size capture|
|100% crop, center of frame||100% crop, center of frame|
|100% crop, top left corner||100% crop, top left corner|