Studio Tests - 35mm full frame

NOTE the line marked 'Nyquist Frequency' indicates the maximum theoretical resolution of the camera body used for testing. Whenever the measured numbers exceed this value, this simply indicates that the lens out-resolves the sensor at this point - the calculated MTF values themselves become meaningless.

The Sony 50mm F1.4 USM gives a somewhat mixed performance on 35mm full-frame, although one that will come as no surprise to anyone experienced at shooting film. It's not as good at large apertures as the Sigma 50mm F1.4 EX DG HSM, which is sharp across a much wider region of the frame. However image quality increases rapidly on stopping down, and optimum results are obtained at about F8. Compared to the Minolta AF 50mm F1.4, the Sony is (as on APS-C) sharper at all apertures, but at the cost of an increased level of chromatic aberration. However the cost of that high central sharpness wide open is also revealed on full frame - corner sharpness never matches the impressive levels achieved by the Canon EF 50mm F1.4 USM (for example) at smaller apertures.

Full-frame compared to APS-C

Eagle-eyed viewers will no doubt have noticed that the MTF50 sharpness data at any particular focal length/aperture combination is higher on full-frame when compared to APS-C. This may at first sight appear unexpected, but in fact is an inevitable consequence of our presentation of the sharpness data in terms of line pairs per picture height (and thus independent of format size).

Quite simply, at any given focal length and aperture, the lens will have a fixed MTF50 profile when expressed in terms of line pairs per millimeter. In order to convert to lp/ph, we have to multiply by the sensor height (in mm); as the full-frame sensor is 1.6x larger, MTF50 should therefore be 1.6x higher.

In practice this is an oversimplification; our tests measure system MTF rather than purely lens MTF, and at frequencies close to Nyquist the camera's anti-aliasing filter will have a significant effect in attenuating the measured MTF50. In addition, our testing procedure involves shooting a chart of fixed size, which therefore requires a closer shooting distance on full frame, and this will also have some influence on the MTF50 data.

Macro Focus

The 50mm behaves rather similarly in our macro test on full frame as on APS-C. Naturally the close focus, working distances and magnification figures remain the same as on APS-C at 44cm, 35cm, and 0.15x respectively, and coverage is 1.5x greater in each dimension. Barrel distortion has become more visible, along with low levels of chromatic aberration. Central sharpness is high but corners are soft at wide apertures, only fully sharpening up at F11.

Macro - 245 x 163 mm coverage Distortion: Moderate barrel Corner softness: Moderate Focal length: 50mm

Specific image quality issues

As 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. We tested the lens primarily on the highly demanding 24Mp full-frame Alpha 900.

Flare

None of the traditional-design 50mm F1.4 lenses we've tested have performed too well with respect to flare, showing all kinds of problems with bright light sources directly within the frame. The Sony 50mm F1.4 is no exception, and shows extensive flare when the sun is placed within the bounds of the frame, with a variety of different patterns dependant upon aperture. The Sigma 50mm F1.4 EX DG HSM fares much better in this regard.

Problems persist when the light source is moved slightly outside the frame, with again an overall loss of contrast and detail. However to be fair the lens regains its poise quickly as the light source is moved further off-axis, and is generally resistant to flare problems in normal shooting situations. And let's not forget the flare-blocking benefits offered by the hood, which Sony users can enjoy without having to pay extra.

F2, Sony Alpha 900	F5.6, Sony Alpha 900
F18, Sony Alpha 900	F2.8, Sony Alpha 900 (sun out of frame)

Background Blur ('bokeh')

One genuinely desirable, but difficult to measure aspect of a lens's performance is the ability to deliver smoothly blurred out-of-focus regions when trying to isolate a subject from the background, generally when using a long focal length and large aperture. The 50mm F1.4 can be made to blur even relatively close backgrounds into oblivion at wide apertures, a huge advantage for portrait shooting especially on APS-C.

The Sony 50mm F1.4 can however produce rather harsh bokeh at wide apertures, with the most attractive results generally achieved when stopped down a bit (F2 - F2.8). In particular, the rendition of distant point light sources can show up as distinctly hard-edged (as shown in the second sample), and under high-contrast conditions, bokeh chromatic aberration can also be very visible (see below).

F2, Sony Alpha 900	50% crop

F1.4, Sony Alpha 900	50% crop, upper right

Chromatic aberration

Lateral chromatic aberration is recorded at a low level in our studio tests, but falls below our informal 0.05% threshold for 'field relevance', and is near-impossible to find in real-world shots. What can be problematic, though, is the presence of quite strong bokeh chromatic aberration, which is most visible at wide apertures, resulting in fringing artifacts in high contrast out-of-focus regions. In the example below we see green fringing in front of the field of focus, with the text taking on a magenta hue; behind the field of focus the situation is reversed.

F1.4, Sony Alpha 900	50% crop, center

In distant backgrounds bokeh CA can show up almost anywhere, as shown in the crops from the samples below. In these examples we again see harsh bright-edged highlights, and the sign in the upper right of the frame (lower left crop) is rendered in a particularly harsh and problematic fashion. In this particular case the double image effect is a classic example of what is often known as 'nisen bokeh' (from the Japanese for 'broken').

F1.4, Sony Alpha 900	50% crop
50% crop	50% crop

In the center of the frame, bright red halation effects can also be observed around in-focus regions, further adding to the colorful, if erroneous rendition of this lens at wide apertures (and even when not obviously visible, still reducing the overall image contrast).

F1.4, Sony Alpha 900	100% crop, center

These factors in combination mean that it is advisable to shoot wide open only when necessary, and in most cases stopping down to F2 - F2.8 will give better results, even when striving for limited depth of field.