Testing: Longitudinal Chromatic Aberration and focus shift
Lenses with focal ratios of f2.8 or larger are often prone to longitudinal color aberrations (loCA, a.k.a. “axial color” or “bokeh CA”). These normally show up as magenta coloration in the foreground and greenish hues in the background and are not easily corrected in post-processing. The Sony shows only a little loCA:
In real life shot I found no purple fringing around high-contrast edges in the focal plane and only some weak green haloing around background subjects.
There’s also no focus shift to worry about although the foreground becomes sharper faster than the background – similar to the Sigma. For comparison see the Sigma 24-70mm f2.8 DG DN Art and the Tamron 28-75mm f2.8 Di III.
Sharpness and contrast
Let’s have a look at the theoretical performance of the Sony FE 24-70mm f2.8 GM first:
These MTF charts show the computed lens-performance of lenses wide open without influence of diffraction. Higher values are better (more contrast) and the closer the line-pairs are together the less astigmatism (= resolution depends on the orientation of the test-pattern) the lens has. The x-axis displays the distance from the optical axis (=center of the sensor) in mm. I’ll show you the real-life performance at 4 mm (center), 13 mm (APS-C-corner), and 20 mm (FF-corner) on a 42MP Sony A7R II body.
From the charts the Sony FE 24-70mm f2.8 GM should have very high contrast (red lines) across the full frame with some softening of small details (green lines) beyond the APS-C image-circle. Let’s see how this theoretical performance translates into real life results in the sharpness test based on Siemens-stars. Processing was done in Lightroom 9.2/CRAW 12.2 from RAW to Adobe Color profile with the built-in lens profile compensating CA and vignetting. Noise-reduction is set to 0, sharpening to 50/0.5/36/10, with no extra tone, color, or saturation adjustment. White-balance was adjusted to a neutral white and I did some exposure compensation to make the brightness of all crops match. So you will not see light fall-off in the corners.
The following are all 100% crops!
First up is an overview of the wide-open performance at different focal lengths. You can jump to the detailed results at different apertures and comparisons with the competition by clicking on the crops of the respective focal length.
Sony’s zoom lens is very sharp in the APS-C image circle up to 35mm becoming a bit softer toward the long end. The FF-corner starts not bad at 24mm but shows signs of astigmatism. This becomes a bit better at 35mm. At 50mm focal length the APS-C corner starts to get softer while the center stays pretty sharp. 70mm is the soft end of the lens. The lens also exhibits some field curvature toward the FF-corner at normal distances.
If you want to see all the details and comparisons with the Tamron 28-75mm f2.8 Di III and Sigma 24-70mm f2.8 DG DN Art, read on. Or you can fast-forward to the performance at long distances.
The following 100% crops for each focal length show the Sony FE 24-70mm f2.8 GM from f2.8 down to f11 plus a comparison with other lenses at f2.8.
Performance at 24mm:
At 24mm focal length the Sony is a little less sharp in the center than the Sigma.
Performance at 28mm:
At 28mm focal length the Sony, Sigma, and Tamron look very similar with a slight edge for the Sigma and Tamron in center sharpness.
Performance at 35mm:
At 35mm there are not many differences in the APS-C image-circle but the FF-corner is much better from the Sony.
Performance at 50mm:
At 50mm focal length the Tamron produces the sharpest image albeit with a little loCA. Stopping the Sony down to f4.0 helps lift the FF-corner visibly.
Performance at 70mm:
At 70mm focal length the Tamron looks best (again) within the APS-C image-circle while the Sony is the softest there. FX-corners of the three lenses all lack definition at f2.8. The Sony profits visibly from stopping down to f5.6.
Performance at long distances
The Siemens-star test-targets are shot at a distance of 45x focal length (i.e. at around 3m for 70mm focal length). But performance of lenses also depends on the shooting distance. Therefore I present another series of test-shots of a city around 1 km away. Processing was done in Lightroom 9.2/CRAW 12.2 from RAW to Adobe Color profile with the built-in lens profile compensating CA and vignetting. Noise-reduction is set to 0, sharpening to 50/0.5/36/10, with no extra tone, color, or saturation adjustment. I used manual focus at the largest aperture and did not change focus for other apertures. All shots were made at ISO 100 and image stabilization switched off.
Following is an overview of the wide-open performance at different focal lengths. You can jump to the detailed results at different apertures and comparisons with other lenses by clicking on the crops of the respective focal length. As usual I have selected the diagonal that provided the better corner results as almost any lens is a bit decentered.
In this long-distance test the Sony is very sharp on the wide end up to 35mm focal length. The drop-off in FF-corner resolution does not look too distracting. At 50mm focal length the APS-C corner starts softening while the FF-corner retains a high definition of fine details. At 70mm the lens becomes visibly softer across the sensor. Even the center loses a bit of its otherwise high contrast.
If you want to see all the details and comparisons with other lenses, read on. Or fast-forward to the next chapter on vignetting and distortions.
The main image shows the complete scene wide open to give you an impression of the angle of view and to judge vignetting. You can access the respective shots up to f11 via the links beneath the main image. Following the main image are 100% crops for each focal length from the Sony FE 24-70mm f2.8 GM down to f11. For comparison I use the Tamron 28-75mm f2.8 Di III and Sigma 24-70mm f2.8 DG DN Art both shot on different days with pretty comparable conditions for the Tamron but higher humidity for the Sigma in the 24mm and 28mm shots reducing overall contrast a bit.
You can click on each image to access the large original. Please respect our copyright and only use those images for personal use.
Results at 24mm:
At 24mm focal length the Sony and the Sigma look pretty similar if you allow for the differences in overall contrast.
Results at 28mm:
The three lenses look pretty similar.
Results at 35mm:
At 35mm the Sony and Sigma look almost indistinguishable in the APS-C image circle but the Sony produces the sharper FF-corner. The Tamron has a comparably sharp center but starts to soften a bit at the APS-C-corner.
Results at 50mm:
While center performance of all three lenses looks comparable the Sony is a bit softer in the APS-C-corner but a bit sharper at the FF-corner than the other two.
Results at 70mm:
At 70mm the Sigma looks sharpest within the APS-C image circle.
Vignetting and distortions
To make it easier to see light fall-off in the corners of a full-frame sensor I’ve arranged a series of three shots each at f2.8, f4.0, and f5.6. All images were developed to the same brightness in the center and are shown with shading compensation set to AUTO:
The sample images above show that with the lens profile applied vignetting is pretty low but not completely eliminated. The automatic shading compensation lifts the extreme corners by about 1 EV at 24mm.
Distortions are of the barrel type at 24mm focal length with a clear mustachio effect and turn to pin-cushion at 70mm. You need to activate the Adobe supplied lens profile to get rid of the distortions in RAW files.
Rendering of point-light sources at night-shots
Night-shots pose a different challenge for lenses as the contrast is even higher than under bright sun and point-light sources can reveal some weaknesses such as coma, haloing and colour-aberrations that do not show up as prominently in other test-shots. The 100% crops below the main image show the effect of coma in the FF-corner of the Sony FE 24-70mm f2.8 GM, the Tamron 28-75mm f2.8 Di III and Nikon Z 24-70mm f2.8 S (Sony FE 24-70mm f2.8 GM coming soon) at various apertures:
On the short end coma is very low at the Sony and Sigma. Only the Tamron shows some.
Coma at 70mm:
At 70mm focal length coma is not very obtrusive with all three lenses.
Rendering of out-of-focus point-light sources
This test is for the rendering of point-light sources in an out-of-focus background. The circle of confusion that is produced by this test is pretty indicative of Bokeh performance (in the background) and light fall-off. Ideally the out-of-focus image of the point-light is evenly lit and perfectly circular, with no “onion-rings”, and without coloration. Large aperture lenses normally produce an effect known as “cat’s eye” the further away from the optical axis the point-light is projected. This is due to optical vignetting in the lens barrel when light enters the lens from an angle.
All images were shot at the longest focal length and largest aperture. The Sony is first followed by the Tamron 28-75mm f2.8 Di III and Sigma 24-70mm f2.8 DG DN Art.
Of the three lenses the Sigma shows the least onion rings and outlining and the Tamron the strongest.
Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf.
The Sony FE 24-70mm f2.8 GM produces the softest background but shows a bit of loCA in the transition zone / middle-ground.
With manual focus the Sony FE 24-70mm f2.8 GM goes down to 1:4.0 magnification at 70mm focal length which is similar to the Sigma 24-70mm f2.8 DG DN Art and Tamron 28-75mm f2.8 Di III. The following images were shot at 1:4 magnification where the area of sharp focus is just 96 x 144mm. The crops shown below are from 0mm, 7mm, and 19mm off the center of the sensor respectively. The Sony produces very usable close-up results once you stop down to f5.6:
This is much better than the Sigma and slightly better than the Tamron.
Flare, ghosting, and sun-stars
Catching a strong light-source shining directly into the lens is always a risky business: it could produce strange colorful ghost-images or reduce contrast considerably through flare and glare. The appearance of flare and ghosting depends on factors like the aperture and the angle of the light hitting the lens. To judge the proclivity of the Sony FE 24-70mm f2.8 GM for these artifacts I went through a series of shots against a strong light source to provoke glare and ghosting.
The Sony FE 24-70mm f2.8 GM has its share of ghost and flare artifacts. At the short end it’s not too bothersome but at the long end it’s more pronounced. Have a look at the following comparison with the Sigma 24-70mm f2.8 DG DN Art:
The little bright square inset in the upper left of both images shows the respective area with an exposure compensation of +3 EV to make it easier to see which levels of black the lens renders at that point. The Sony FE 24-70mm f2.8 GM looks similar to the Sigma 24-70mm f2.8 DG DN Art.
When the light-source is just outside the corner there is a strong streak/flare at 70mm focal length. Fortunately this only happens in a very small area around the corners. And at 24mm it’s not a problem.
To produce nice sunstars with the Sony FE 24-70mm f2.8 GM stop down at least to f8:
Next check out my sample images!Check prices on the Sony FE 24-70mm GM at Amazon, B&H, Adorama, or Wex. Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!