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Sony FE 24mm f/1.4 GM (SEL24F14GM) - Review / Test Report - Analysis |
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Lens Reviews -
Sony Alpha (Full Format)
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Page 2 of 3
Distortion
Many "mirrorless" lenses aren't fully corrected in terms of image distortions. However, Sony went the extra mile with the Sony FE 24mm f/1.4 GM. With a pincushion distortion of just under ~0.5%, there's already nothing to complain about in RAW mode. The remaining traces can be eliminated in auto-correction mode.
Vignetting
Vignetting can be an issue in RAW mode and it is somewhat worse than usual in this lens class. At f/1.4 the light falloff is rather massive at 2.7EV (f-stops). Stopping down helps, of course, but the vignetting remains visible at around 1.5EV - probably a side effect of the rather small front element and an indication that Sony is relying on its image auto-correction capabilities in this respect. With activated auto-correction, you can still spot some light falloff at f/1.4 albeit it's far from being extreme in this case. The issue is pretty much negligible by most standards from f/2.8 onward.
MTF (resolution)
The resolution characteristic is very impressive for such a fast lens. Typically f/1.4 lenses struggle at fully open aperture but the Sony lens manages to maintain a decent level of quality. The image center is dead sharp here and the near-center is very good. The borders/corners are, of course, softer but they don't dive into a deep abyss at least. Stopping down to f/2 results in a general increase in quality and even the corners make it to good levels. It is worth noting that the center quality at f/2 is already exceeding the resolution of the 42mp sensor used for this test. The peak performance is reached around the f/4 mark with an outstanding center, an excellent broader center and a very good outer image region. Diffraction effects are starting to kick in at f/8 - albeit without limited impact. It's getting more pronounced from f/11 onward though.
The field curvature is low. The centering quality of the tested sample was Ok.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness.
If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations
Chromatic Aberrations (CAs)
On Sony cameras, you don't really have to worry about chromatic aberrations due to image auto-correction. However, even if you prefer to disable this for whatever reason, the CAs are fairly low at around 1px on the average at the image borders.
Bokeh
Sony is stressing that the Sony FE 24mm f/1.4 GM isn't just about excellent sharpness but it is also supposed to be capable of rendering a beautiful bokeh (out-of-focus blur). Generally, we agree with this - with one caveat.
When observing the focus transition zones, the bokeh is very smooth in the image background (shown to the left below). The less critical foreground blur (to the right) is rather harsh with double halos (nisen bokeh) though.
Out-of-focus highlights are almost perfect with a smooth inner zone and basically no outlining at the edges of the discs. The circular shape of the discs remains intact even when stopped down to f/2.8 - surely a positive impact from the 11 aperture blades.
Another positive surprise is the rendering of the highlight discs towards the borders/corners. Normally the shape of the discs deteriorates substantially - often into "cat eyes". However, the Sony lens is -almost- capable of maintaining circular discs here (Note: you may notice some "highlight shadows" in the sample images below - these relate to the LED diodes with their non-perfect shape). As usual, stopping down corrects the shape a little.
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