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 show up as magenta coloration in the foreground and greenish hues in the background and are not easily corrected in post-processing. The Sony 16-35mm f2.8 GM is very good in this respect: there is almost no loCA to be seen at f2.8.
There is also no focus shift when stopping down. For comparison have a look at the Tamron 17-28mm f2.8 Di III here which also has very little loCA but exhibits some focus shift.
Sharpness and contrast
Let’s have a look at the theoretical performance of the Sony FE 16-35mm f2.8 GM first and compare it to the performance of the Tamron 17-28mm f2.8 Di III:
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 solid and the dotted lines 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.
From the charts the Sony FE 16-35mm f2.8 GM should be very good with only a mild decline in sharpness towards the full-frame corner. But the lens develops quite some astigmatism especially beyond 12mm image-height. Let’s see how this theoretical performance translates into real life results in the sharpness test based on Siemens-stars at 4 mm (center), 13 mm (APS-C-corner), and 20 mm (FF-corner) off axis. Processing was done in Lightroom 8/CRAW 11 from RAW to Adobe Color profile with the built-in lens profile for shading and CA compensation applied. Distortion compensation is currently not recognized by Adobe’s RAW converter. 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 Sony FE 16-35mm f2.8 GM by clicking on the crops of the respective focal length.
The Sony GM produces a very sharp center and a slightly softer APS-C-corner throughout the zoom-range. The FF-corner also looks pretty good even wide open with peak performance at 20mm and 24mm and some astigmatism at the other focal lengths.
If you want to see all the details and comparisons with the Tamron 17-28mm f2.8 Di III, 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 16-35mm f2.8 GM from f2.8 down to f11 compared to the Tamron 17-28mm f2.8 Di III at f2.8.
Performance at 17mm:
The Sony is sharper wide open than the Tamron in the center and the FF-corner while APS-C-corner performance is comparable. Stopping the Sony GM down to f5.6 get’s rid of the astigmatism in the FF-corner.
Performance at 20mm:
At f2.8 the Sony GM is crisper across the full-frame sensor than the Tamron. You can easily use it wide open and get very good results.
Performance at 24mm:
At 24mm focal length the Tamron has a slight lead in the center over the Sony GM which is still slightly sharper towards the corners. Stopping the Sony GM down to f4.0 produces a very sharp center too. For best full-frame corners stop further down to f5.6.
Performance at 28mm:
Both the Sony GM and the Tamron look pretty comparable within the APS-C image-circle wide open. The Sony GM has the lead in the FF-corner but still could profit from stopping down to f4.0 or f5.6 to reduce the effect of astigmatism.
Performance at 35mm:
No comparison with the Tamron at 35mm focal length. The FF-corner of the Sony GM profits clearly from stopping down to f5.6 to eliminate the blurring from astigmatism.
Performance at long distances
The Siemens-star test-targets are shot at a distance of 45x focal length (i.e. at around 1.5m for 35mm 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 8/CRAW 11 from RAW to Adobe Color profile with no correction for distortions. 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.
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 Tamron 17-28mm f2.8 Di III 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 FE 16-35mm f2.8 GM looks very sharp at the short end up to 20mm focal length. At 24mm the FF-corner loses a bit of its acuity and becomes progressively softer towards the long end. And the APS-C-corner looks a bit softer too at 28mm and 35mm.
If you want to see all the details and comparisons with the Tamron 17-28mm f2.8 Di III, read on. Or fast-forward to the next chapter on vignetting.
The main image shows the complete scene wide open to give you an impression of the angle of view and to judge vignetting. Following the main image are 100% crops for each focal length from the Sony FE 16-35mm f2.8 GM down to f11 compared to the Tamron 17-28mm f2.8 Di III at f2.8. Both lenses were shot on the same day within minutes of each other. You can access the full resolution shots up to f11 via the links beneath the main image or clicking on the respective crops. Please respect our copyright and only use those images for personal use.
Results at 16mm:
The Tamron and the Sony look very similar in this comparison with a slight advantage for the Sony in the FF-corner.
Results at 20mm:
Again both lenses perform very similar.
Results at 24mm:
The Tamron produces the crisper APS-C-corner and FF-corner at 24mm than the Sony.
Results at 28mm:
At 28mm the Tamron again beats the Sony at the APS-C and FF-corner. The APS-C-corner of the Sony GM sharpens up nicely at f4.0 but the FF-corner still stays a bit soft.
Results at 35mm:
At 35mm the Sony GM again profits from stopping down to f4.0 or even f5.6 to give acuity outside the center a lift.
In this long distance comparison the Sony FE 16-35mm f2.8 GM looks very similar to the Tamron at the short end but is a bit softer at 24mm and 28mm. And 35mm certainly is the weakest focal length of the Sony GM lens.
Vignetting and distortions
Vignetting and distortions are lens aberrations that can be easily corrected by software. Lightroom and Photoshop have offered lens profiles for some time which could be applied as an option. With most mirrorless systems though, Adobe applies lens profiles automatically whether you want them or not. But on Sony Alpha mirrorless cameras you can switch lens compensation off separately for vignetting, colour aberrations, 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 with the Sony GM at different apertures. All images were developed to the same brightness in the center. The first line shows vignetting at 16mm focal length, the second at 35mm both without extra shading compensation from the Adobe lens profile:
The sample images above show that the lens produces quite some vignetting at the short end wide open but you can always apply some compensation through the Adobe lens profile.
Distortions are of the barrel type at 16mm with a strong mustachio effect and turn to pin-cushion from 24mm focal length onward. The lens profile corrects the distortions nicely whether for in-camera JPGs or through Adobe’s RAW-converter. At the end of the samples page there are images at different focal length that show the distortions of uncorrected RAWs developed in Lightroom versus corrected JPGs straight out of camera with lens profile applied.
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 at the short end of the Sony FE 16-35mm f2.8 GM and the Tamron 17-28mm f2.8 Di III at various apertures:
On the short end the Sony FE 16-35mm f2.8 GM has very little coma already wide open similar to the Tamron 17-28mm f2.8 Di III.
Coma at the long end:
Same at the long end: both lenses show very little coma.
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 FE 16-35mm f2.8 GM is first followed by the Tamron.
Shot at 35mm, f2.8 the Sony GM should produce Bokeh balls that are 25% larger in diameter than from the Tamron 17-28mm f2.8 Di III at 28mm, f2.8. This difference is not fully reflected in the test-shots above as focus/magnification was not set exactly comparably. Comparing the other qualities the 17-28mm f2.8 Di III shows the brighter outline and stronger onion rings than the Sony GM. The cat’s eye effect is relatively mild on both lenses and Bokeh balls remain pretty circular when stopped down to f8.0.
Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf at 35mm.
As was to be expected Bokeh is not very pronounced with a lens of such short focal length and a focal ratio of only f2.8. Still the Sony FE 16-35mm f2.8 GM profits in this comparison against the Tamron a little from its longer focal length. But other than that the Sony’s Bokeh does not look much better than from the Tamron.
The Sony FE 16-35mm f2.8 GM can achieve quite a good magnification of around 1:5 at closer distances. Below you can see how the lens performs in close-up shooting at 35mm focal length. The images were shot at 1:5.3 magnification where the area of sharp focus is just 126 x 189mm. The crops shown below are from 0mm, 12mm, and 21mm off the center of the sensor respectively:
The Sony FE 16-35mm f2.8 GM produces very usable results in the APS-C image-circle even at f2.8. But for shooting flat subjects it’s better to stop down to f8.0 as the lens exhibits quite some field-curvature at such close distances – which I tried to compensate for in the above test-shots by tilting the camera slightly off the perfectly perpendicular position.
Flare, ghosting, and sun-stars
Catching a strong light-source shining directly into the lens is always a risky business: it could produce strange colourful 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. So to judge the proclivity of the Sony FE 16-35mm f2.8 GM for these artefacts I went through a series of well calculated shots against a strong light source to provoke glare and ghosting. The lens hood was mounted in all shots.
In the following images the little bright square inset in the upper left 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 16-35mm f2.8 GM renders a deep black with little veiling glare and is mostly clear of flare and glare artefacts when the light-source is in the frame. But when the light-source is outside the frame I found multiple instances/angles at 35mm focal length where streaks/flares develop. This is a bit different from many other lenses: those often develop one brighter streak but only at a very narrow angle right at the corner of the frame.
My tests also show that sun-stars of the Sony FE 16-35mm f2.8 GM are well defined at the wide end of the lens while they lose some of their definition at 35mm focal length.
Next check out my sample images!Check prices on the Sony FE 16-35mm f2.8 GM at Amazon, B&H, or Adorama, or Wex. Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!>