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 Viltrox shows some loCA from f1.8 to f2.8, less than the Sony FE but more than the Z Nikkor.
When stopping down the background becomes sharper much faster than the foreground which is indictive of a slight focus shift. For comparison have a look at the Nikon Z 85mm f1.8 S and Sony FE 85mm f1.8.
The following real life shots show that loCA from the Viltrox could be very visible:
Sharpness and contrast
Let’s have a look at the theoretical performance of the Viltrox AF 85mm f1.8 II and compare it to the performance of the Nikon Z 85mm f1.8 S and Sony FE 85mm f1.8:
The MTF charts of the Viltrox, Nikon and Sony lenses show the computed contrast-curves at 10 line-pairs/mm and 30 lp/mm without influence of diffraction while Zeiss shows the measured contrast of the Batis at 10, 20 and 40 line-pairs per mm (incl. diffraction). Higher values are better (more contrast) and the closer the dotted and solid lines are together the less contrast dependents on the orientation of the test-pattern (less astigmatism). 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/DX-corner), and 20 mm (FF/FX-corner) on a 45MP Nikon Z7 body.
From the charts the Viltrox AF 85mm f1.8 II looks quite similar to the Sony FE but the Z-Nikkor should clearly best it – at least up until 20mm image-height. The MTF-chart from Zeiss is harder to compare but I’d guess the Batis performs somewhat between the Z-Nikkor and the other two lenses.
Let’s see how this theoretical performance of the Viltrox translates into real life results in the sharpness test based on Siemens-stars. Processing was done in Lightroom 10.1/CRAW 13.1 from RAW to Adobe Color profile with the built-in lens profile for Vignette Control and CA compensation 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 Viltrox AF 85mm f1.8 II from f1.8 down to f11 compared to the Nikon Z 85mm f1.8 S (both shot on a Nikon Z7) and Sony FE 85mm f1.8 shot on a Sony A7R II at f1.8. With linear resolution of the 45MP Z7 sensor only 4% higher than from the 42MP A7R II, identical test set-up and identical RAW processing the comparability between the test-shots should be very good.
At f1.8 the Viltrox AF 85mm f1.8 II looks less sharp than the Nikon Z 85mm f1.8 S but sharper than the Sony FE 85mm f1.8 across the full-frame sensor. The Viltrox shows quite some field-curvature between the center and the APS-C/DX-corner. Stopping down to f2.8 or f4.0 sharpens the lens up nicely but from f8 onward the lens softens again.
Performance at long distances
The Siemens-star test-targets are shot at a distance of 45x focal length (i.e. at around 4m for 85mm 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 10.2/CRAW 13.2 from RAW to Adobe Color profile with the lens-profile applied. 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 base ISO and image stabilization switched off.
The following image shows the complete scene wide open to give you an impression of the angle of view. Following the main image are 100% crops from the center, APS-C/DX-corner, and FF/FX-corner from the Viltrox AF 85mm f1.8 II compared to the Nikon Z 85mm f1.8 S and Sony FE 85mm f1.8 at f1.8. The three lenses were shot at different days – but with roughly comparably atmospheric conditions. As usual I have selected the diagonal that provided the better corner results as almost any lens is a bit decentered.
You can access the large originals but please respect our copyright and only use those images for personal use.
The Viltrox AF 85mm f1.8 II and the Nikon Z 85mm f1.8 S are very close with the Z Nikkor producing the sharper DX-corner and the Viltrox the sharper FF/FX-corner. The Sony FE 85mm f1.8 is certainly softer in the APS-C image-circle than the other two lenses suffering from some green and magenta halos at high contrast edges but its FF-corner is pretty good.
Let’s see how the Viltrox develops when stopped down:
Stopping the Viltrox AF 85mm f1.8 II down to f2.8 and f4.0 visibly lifts acuity in the APS-C/DX- and FF/FX-corner to very good sharpness.
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 shots with the Viltrox AF 85mm f1.8 II at different apertures. All images were developed to the same brightness in the center.
The sample images above show that with the lens profile applied vignetting of the Viltrox is relatively mild wide open. Vignette control set to Normal lifts the extreme corners about 0.5 EV at f1.8. Adobe’s RAW converter automatically applies shading compensation as it was set in camera – but you cannot alter the setting in postprocessing.
That’s different with distortions: Adobe’s RAW converter ignores what was set in camera and always corrects them. Pin-cushion distortions are very visible if not corrected and are still visible when Auto distortion control is set to ON. If you want to reduce the remaining distortion manually dial in an extra -4 in Lightroom 10.2 / CRAW 13.2. There’s also a lens profile which can be downloaded from the Viltrox web-site and integrated in Photoshop for RAW files/JPGs and Lightroom (only for JPGs), but it is a hassle to use.
Distortions from top to bottom: Viltrox AF 85mm f1.8 II, as is / with lens-profile / with an extra -4 manual correction
One final remark regarding the Vitrox lens profile: Although Adobe’s RAW converter recognizes the profile to include lateral CAs correction they were still pretty visible. So it’s best to manually activate CA reduction in Lightroom / CRAW in addition to what the lens profile already does. All test-shots above were developed this way.
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/FX-corner of the Viltrox at various apertures:
The Viltrox AF 85mm f1.8 II shows a bit more coma wide open than the Nikon Z 85mm f1.8 S but less than the Sony FE. It becomes well controlled at f2.8. Looking at the point-lights near the center reveals a bit of purple/blue fringing at f1.8. But it is much less than the Sony FE produces and is visibly reduced at f2.0 already and gone at f2.8.
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.
The crops below the main image are from the center, APS-C/DX-corner, and FF/FX-corner resized to make them comparable across all my reviews.
The diameter of the Bokeh balls in the center is determined by the entrance pupil of the lens. So all 85mm f1.8 lenses produce Bokeh balls that are the same size at identical magnifications. Compression of the circle towards the corners looks relatively mild at f1.8 and is completely gone at f4.0. Unfortunately the aperture blades of the Viltrox are not well-rounded and show up already at f2.8. The inside of the Bokeh balls is very smooth but there is some outlining combined with visible color aberrations in the rim.
Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf.
All three lenses look pretty similar in the foreground and background. In the middle-ground color aberrations from the Viltrox are a bit stronger than from the Z Nikkor but better than from the Sony FE.
Looking at another crop (now at 100%) from the same images showing the ruler has the Viltrox and the Z Nikkor look pretty similar while the Sony FE produces a harsher transition than the other two lenses.
If you’re curious how this all shapes up when shooting portraiture have a look at the samples section on the next page.
Flare, glare, 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 new Viltrox AF 85mm f1.8 II for these artifacts 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. Following are some of the more extreme example results. 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:
Ghosting seems relatively well controlled on the Viltrox but flare and glare is certainly not – regardless of aperture. The risk of reduced black levels and strange flares is pretty high against strong contra light. Even if the light source is just outside the corner as in the following three examples:
The Viltrox AF 85mm f1.8 II produce well defined sunstars already at f4. And the more you stop down the bigger they get:
Next check out my sample images!Check prices on the Viltrox AF 85mm f1.8 II at Amazon, B&H or Adorama. Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!