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 FE 85mm f1.8 is no exception: it shows quite some loCA even up to f4.0. 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 Sony FE 85mm f1.8 first and compare it to some alternatives from Zeiss 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 Sony FE 85mm f1.8 should perform similarly to the Zeiss 85mm f1.8 Batis with the Tamron seemingly besting both of the other two. But let’s see how this theoretical performance of the Sony translates into 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 Sony FE 85mm f1.8 from f1.8 down to f11 compared to the Zeiss 85mm f1.8 Batis, 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 Sony FE 85mm f1.8 is clearly bested by all other lenses: It is the softest in the center and it shows astigmatism at the APS-C corner. Its FF-corner is not too bad, similar to the Zeiss Batis, but the Tamron and the Sigma show how a good FF-corner should look like.
Now let’s see how the Sony FE 85mm f1.8 develops when stopped down:
Stopping Sony’s FE 85mm f1.8 down helps the center sharpen up nicely at f2.8 and the APS-C-corner shed the effects of astigmatism at f4.0.. Only the FF-corner needs stopping down to f8.0. But for the intended use of this lens sharp FF-corners may not be necessary.
For the cheapest lens in this comparison the performance is respectable. But it also shows that you get what you pay for: The more expensive lenses show a clear advantage in this test.
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 Sony FE 85mm f1.8 down to f11 compared to the Zeiss 85mm f1.8 Batis 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 Sony FE 85mm f1.8 is again bested by the Zeiss Batis in the center and the APS-C-corner but seems a bit sharper in the FF-corner than the Batis! Let’s see how the Sony FE 85mm f1.8 develops when stopped down:
Stopping down to f2.8 or f4.0 improves performance quite a bit and makes the Sony FE 85mm f1.8 fit for capturing very finely details scenes.
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 Sony FE 85mm f1.8 and the Zeiss 85mm f1.8 Batis 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 sample images above show that with the lens profiles applied vignetting still remains visible even at f4.0. But the Sony has a relatively mild vignette wide open in comparison to the Zeiss Batis.
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 85mm f1.8 and the Zeiss Batis at various apertures:
Both lenses produce similar amounts of coma which is not very disturbing from f2.8 onward. But the Sony shows some annoying magenta haloing around bright lights as you can see in the following crop from near the center of the image:
The Sony FE 85mm f1.8 needs to be stopped down to f2.8 to avoid this effect.
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.
The main take-away from this test: The Sigma 85mm f1.4 Art easily 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. That being out of the way the remaining three f1.8 lenses still show some differences: of the three 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 Sony FE 85mm f1.8 for these artefacts I went through a series of well calculated shots against a strong light source to provoke glare and ghosting.
The Sony FE 85mm f1.8 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 Sony FE 85mm f1.8 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 Sony FE 85mm f1.8 at Amazon, B&H, Adorama, or Wex. Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!