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 Zeiss 85mm f1.8 Batis is no exception: it shows quite some loCA up to f2.8. The following 100% crops show the foreground on the left and the background on the right with the first crop at 1.8, second at f2.8, third at f4.0:
The test also revealed that there is no focus shift to speak of at distances of 3.5m and farther away.
Sharpness and contrast
Let’s have a look at the theoretical performance of the Zeiss 85mm f1.8 Batis first and compare it to some alternatives from Sony and Tamron:
The MTF chart of the Zeiss Batis (middle) shows the measured contrast wide open at 10, 20 and 40 line-pairs per mm. This includes the influence of diffraction unlike the computed MTF charts from Sony (left) and Tamron (right) showing contrast at 10 lp/mm and 30 lp/mm. 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. Note: Ignore the red/orange lines in Sony’s MTF chart for this comparison as they represent the results stopped down to f8. 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 Zeiss 85mm f1.8 Batis should have a clear disadvantage compared to the Sony and Tamron lenses. But keep the differences between methodology of these MTF-charts in mind and we’re probably not seeing a proper apples-to-apples comparisons here. So let’s turn to real life results in the 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. Removal of lateral color aberrations is ON, longitudinal CA are not corrected.
The following 100% crops show the Zeiss 85mm f1.8 Batis from f1.8 down to f11 compared to the Sony FE 85mm f1.8, the Tamron 85mm f1.8 VC, and Sigma 85mm f1.4 Art at f1.8. The Tamron and the Sigma were shot on a 36MP D810 with no lens profiles applied. The linear resolution of the Nikon D810 sensor is only 7% lower which should not make a visible difference in this comparison.
In this comparison at f1.8 the Batis shows that’s it a clear step-up over the Sony FE 85mm f1.8: It is sharper in the center and shows less astigmatism at the APS-C corner. It’s also a bit better in the FF-corner than the Sony but the Tamron and the Sigma show how a good FF-corner should look like.
Now let’s see how the Zeiss 85mm f1.8 Batis develops when stopped down:
Stopping the Zeiss Batis down helps sharpen up the FF-corner nicely until at f4.0 the performance is very good across the full-frame sensor.
Performance at long distances
The Siemens-star test-targets are shot at a distance of 45x focal length (i.e. at around 4m). 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 the lens-profile for distortion and vignetting 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 were made at ISO 100 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 85mm f1.8 Batis down to f11 compared to the Sony FE 85mm f1.8 at f1.8. The lenses were shot on the same day only minutes apart.
You can click on each image to access the large original. Please respect our copyright and only use those images for personal use.
The Zeiss Batis again has a clear lead over the Sony FE 85mm f1.8 in the center and the APS-C-corner but seems a bit softer in the FF-corner than the Sony. Let’s see how the Zeiss 85mm f1.8 Batis develops when stopped down:
Stopping down to f2.8 or f4.0 improves performance of the FF-corner to good resp. very good.
To make it easier to see light fall-off in the corners of a full-frame sensor I’ve arranged a series of shots with the Zeiss 85mm f1.8 Batis and the Sony FE 85mm f1.8 at different apertures. All images were developed to the same brightness in the center and the integrated lens profiles applied, Shading Compensation in camera was set to Auto:
The Zeiss Batis has the stronger vignette wide open compared to the Sony. The sample images above also show that with the lens profiles applied vignetting still remains visible even at f4.0 on both lenses.
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 Zeiss Batis and the Sony FE 85mm f1.8 at various apertures:
Both lenses produce similar amounts of coma which is not very disturbing from f2.8 onward. But the Zeiss Batis shows much less magenta haloing around bright lights than the Sony as you can see in the following 100% crops from near the center of the image:
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.
Both lenses produce very similar Bokeh balls: The size is equal, the cats eye effect is clearly visible even in the APS-C-corner at f1.8, outlining is very moderate and almost free of color, and there are no onion rings.
Let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf.
As you can clearly see the Sigma 85mm f1.4 Art beats the other f1.8 lenses when used wide open. Even though its focal ratio is only 2/3 of a stop brighter there is no denying that it produces the creamier foreground, middle-ground and background Bokeh. Of the three f1.8 lenses the Tamron seems the most color-neutral in the middle-ground, and the Sony seems to have a slightly softer fore- and background than the Zeiss Batis.
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 Zeiss 85mm f1.8 Batis for these artefacts I went through a series of well calculated shots against a strong light source to provoke glare and ghosting.
The Zeiss 85mm f1.8 Batis is quite prone to flare and ghosting artefacts. 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 clearly shows that the Zeiss 85mm f1.8 Batis also suffers from quite some veiling glare. And you better watch out, when the light-source is just outside the corner:
The lens produces nice sunstars even at f5.6 and more so when you stop down further:
Next check out my sample images!Check prices on the Zeiss Batis 85mm f1.8 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!