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. But the Zeiss Batis 40mm f2.0 CF is very good in this respect: it shows very little loCA even wide open. The following 100% crops show the foreground on the left and the background on the right with the first crop at f2.0, second at f2.8, third at f4.0:
As you can see in the following example there is no discernible coloration around the foreground or background branches:
The test also revealed that there is no focus shift to speak of.
The Sigma 40mm f1.4 Art also has very little loCA (see here, crops are f1.4, f2.0, f2.8) while the Sony 35mm f1.4 ZA (here) shows the effect pretty prominently. The Sony 35mm f2.8 ZA is also not the best regarding loCA considering that it has a focal ratio of only f2.8 (see here, crops are f2.8 and f4.0).
Sharpness and contrast
Let’s have a look at the theoretical performance of the Zeiss Batis 40mm f2.0 CF first and compare it to the alternatives from Sigma and Sony:
The MTF charts of the Zeiss (designed) lenses from Zeiss and Sony show the contrast wide open at 10, 20 and 40 line-pairs per mm. This includes the influence of diffraction on the Zeiss Batis and probably on the Sony 35mm f1.4 ZA but certainly not on the Sony 35mm f2.8 ZA – which makes the MTF-charts of the latter look better in comparison. The computed MTF chart of the Sigma Art shows contrast at 10 lp/mm and 30 lp/mm at f1.4 without influence of diffraction. Higher values are better (more contrast) and the closer the solid and 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. 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 (resp. 46MP Nikon Z7 for the Sigma Art).
From the charts the Sigma 40mm f1.4 Art looks clearly better than every other lens in this comparison and the Sony 35mm f2.8 ZA has the steepest drop in contrast towards the corners. But other than that the different methodologies and the different focal ratios used in these charts makes it hard to compare the lenses. So let’s see how these lenses perform in my sharpness test based on Siemens-stars. Processing was done in Lightroom 8/CRAW 11 from RAW to Adobe Color profile with the built-in lens profile applied. 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 100% crops show the Zeiss Batis 40mm f2.0 CF from f2.0 down to f11 compared to the Sony 35mm f1.4 ZA and the Sony 35mm f2.8 ZA (all shot on a 42MP Sony A7R II at ISO 100) plus the Sigma 40mm f1.4 Art (shot on a 46MP Nikon Z7 with FTZ-adapter at ISO 64). As the linear resolution of the Z7 sensor is only 4% higher than from the Sony A7R II this should not make a distinct difference in this comparison.
In this comparison at f2.0 the Zeiss Batis is almost as sharp in the center and the FF-corner as the excellent Sigma Art but its APS-C-corner is clearly softer. The Sony 35mm f1.4 ZA is also very sharp in the center but its corners look mushy in comparison.
Let’s do the same comparison at f2.8 now including the Sony 35mm f2.8 ZA:
At f2.8 the Sony 35mm f2.8 ZA slots in slightly better than the Sony 35mm f1.4 ZA. But the Sigma Art and the Zeiss Batis still lead by a clear margin.
Now let’s see how the Zeiss Batis 40mm f2.0 CF develops when stopped down further:
Stopping the Zeiss Batis 40mm f2.0 CF further down make the slight softness at the APS-C-corner disappear completely at f5.6 until you clearly get softening from diffraction at f11.
Performance at long distances
The Siemens-star test-targets are shot at a distance of 45x focal length (i.e. at around 1.8m). But as performance of lenses also depends on the shooting distance I did 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 the lens-profile automatically applied. Noise-reduction is set to 0, sharpening to 50/0.5/36/10, with no extra tone, color, or saturation adjustment. I used autofocus at the largest aperture and did not change focus for other apertures. All shots of the Sigma 40mm f1.4 Art were made on a 46MP Nikon Z7 (with FTZ-adapter) at ISO 64 and image stabilization switched off.
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 from the Zeiss Batis 40mm f2.0 CF from f2.0 down to f11 compared to the Sony 35mm f1.4 ZA and the Sony 35mm f2.8 ZA (all shot on a 42MP Sony A7R II at ISO 100) plus the Sigma 40mm f1.4 Art (shot on a 46MP Nikon Z7 with FTZ-adapter at ISO 64). All lenses were shot on the same day only minutes apart. The small differences in linear resolution between the Nikon and the Sony camera should not cause a visible difference in sharpness.
You can click on each image to access the large original. Please respect our copyright and only use those images for personal use.
Wide open the Zeiss Batis 40mm f2.0 CF again resolves very fine details across the sensor but the center crop suffers a little from glare that reduces edge contrast a bit. The Sigma Art produces the slightly better center and FF-corner but seems to lag a bit in the APS-C-corner. The Sony 35mm f1.4 ZA also produces a very sharp center and a pretty good FF-corner only slightly behind the Zeiss Batis. But its APS-C-corner is even less well defined than from the Sigma Art as field curvature bends the focal plane towards the camera (see the sharp looking branch in the foreground of the middle crop).
Let’s repeat the comparison at f2.8 now including the Sony 35mm f2.8 ZA:
At f2.8 the Zeiss Batis is now almost indistinguishable from the Sigma Art inside the APS-C image-circle. But its FF-corner does not seem to profit much from stopping down. The Sony 35mm f2.8 ZA trails behind the other lenses in this comparison with a generally softer rendering. I had to take the other diagonal of the image in this comparison, as the little lens was quite decentered.
Following is how the Zeiss Batis 40mm f2.0 CF develops when stopped down:
At f5.6 the Zeiss Batis 40mm f2.0 CF reaches excellent performance across the full-frame sensor.
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 color-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 Zeiss Batis 40mm f2.0 CF, Sigma 40mm f1.4 Art, Sony 35mm f1.4 ZA, and the Sony 35mm f2.8 ZA at various apertures:
Both the Zeiss Batis (at f2.0) and the Sony 35mm f1.4 ZA (at f1.4) show some coma deforming point-light sources into birdlike apparitions. The Sigma Art produces almost no coma wide open while the Sony 35mm f2.8 ranks last – although it has the slowest focal ratio.
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.
Of the four lenses in this comparison the Sigma clearly produces the nicest, smoothest Bokeh balls with no onion rings and only a little outlining that shows no coloration from loCA. The Zeiss Batis and both Sony ZA lenses show visible onion-rings and the Zeiss Batis and the Sony 35mm f2.8 ZA also have some outlining. Compression of the Bokeh balls is visible in the APS-C-corner already with all four lenses but the Zeiss Batis retains a more circular form while the Sigma Art and the Sony 35mm f1.4 ZA produce the typical cat’s eye. The Zeiss Batis has 1/3 smaller Bokeh balls in the center compared to the Sigma Art due to its f2.0 focal ratio. In the image above the difference is overstated as I did not set the focus on the Zeiss Batis correctly for this comparison.
Let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf.
From the comparison above it is clear that the large focal ratio (potentially) produces the better Bokeh: the Sigma Art leads in this comparison followed by the Sony 35mm f1.4 ZA which is a little harsher in the middle-ground and background. The Zeiss Batis is hampered by its f2.0 focal ratio and shows some outlining in the background. Last comes the Sony 35mm f2.8 ZA which simply cannot compete with the other lenses in this comparison.
The Zeiss Batis 40mm f2.0 CF goes down to 1:3.1 magnification which is better than any other lens in this comparison. And its performance is very good. Even the outer areas are quite usable wide open. The following image was shot at 1:3.5 magnification where the area of sharp focus is just 84 x 126mm. The crops shown below are (from left to right) from 4mm, 12mm, and 19mm off the center of the sensor respectively:
But there is a trick by which the Zeiss Batis achieves these results: It’s effective aperture is not what is shown in the display or recorded in the EXIF data when shooting very close-up. So if you think you shoot at f2.0 the lens stops a bit down providing a slightly deeper dof and better resolution than it would achieve otherwise. This also reduces the roundness of out-of-focus highlights (Bokeh balls) as the aperture is not perfectly circular when stopped down from f2.0. Zeiss is currently working on a software update to limit this effect to nominal aperture values of between f2.0 and f2.8 and limit the automatic stop-down to f2.8. Keep in mind that this only happens in (very) close-up shooting.
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. So to judge the proclivity of the Zeiss Batis 40mm f2.0 CF for these artifacts I went through a series of well calculated shots against a strong light source to provoke glare and ghosting.
The Zeiss Batis 40mm f2.0 CF is a bit prone to flare and glare. The following image at f11 is one of the most obvious examples:
The little square inset in the upper left of the image 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. It shows that the Zeiss Batis 40mm f2.0 CF does not render the deepest black against contra light. Turn the camera just a bit and the glare around the light source is considerably reduced and the black becomes deeper although the flares remain the same:
When the light-source is just outside the corner the resulting streak is very obvious. But this only happens in a very small area around the corners.
All-in-all the Zeiss Batis needs a bit of attention when shooting under adverse contra-light situations.
Sunstars develop already at f2.8 as the aperture is no longer perfectly circular:
Next check out my sample images!Check prices on the Zeiss Batis 40mm f2 at Amazon, B&H, Adorama or WEX! Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!