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 a bit of loCA up to f2.8 but is a little better than the Nikon Z 24mm f1.8 Z.
When stopping down the background and foreground become equally sharper and there’s no focus shift.
Sharpness and contrast
Let’s have a look at the theoretical performance of the Viltrox AF 24mm f1.8 and compare it to the performance of the Nikon Z 24mm f1.8 S, Sigma 24mm f2 DG DN, and Sony FE 24mm f2.8 G:
The MTF charts show the computed contrast-curves at 10 line-pairs/mm and 30 lp/mm without influence of 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 24mm f1.8 (at f1.8, black lines) looks clearly worse wide open than the other three lenses. Even stopping the Viltrox down to f8.0 (blue lines) makes it look only slightly better at 30 lp/mm than the Z-Nikkor at f1.8.
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 11.4.1/CRAW 14.4.1 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 24mm f1.8 from f1.8 down to f11 compared to the Nikon Z 24mm f1.8 S. As the Viltrox was quite decentered I chose the better image quadrant for this test. This might overstate the image quality of a perfectly centered copy of this lens.
The center of the Viltrox AF 24mm f1.8 looks quite sharp even at f1.8 albeit with a bit of loCA. At f4.0 the center is very sharp. The APS-C/DX-corner of the Viltrox is less well defined wide open and does not respond quickly to stopping down: Only at f8.0 does it improve to a satisfying acuity. The FF/FX-corner lacks overall contrast wide open due to coma but still shows a surprising level of detail. Contrast improves quickly and at f2.8 the FF/FX-corner looks good. Stopping further down reveals lateral color aberrations although the integrated lens-profile should have dealt with them. The Nikon Z 24mm f1.8 S in comparison has the much better DX-corner and also better contrast and less coma in the FX-corner – albeit it resolves a bit less detail than the Viltrox there. Field-curvature of the Viltrox is quite low between the center and the APS-C/DX-corner but stronger towards the FF/FX-corner.
Performance at long distances
The Siemens-star test-targets are shot at a distance of 45x focal length (i.e. at around 1m for 24mm 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 11.4.1/CRAW 14.4.1 from RAW to Adobe Color profile with the Adobe lens-profile applied to reduce distortions and light fall-off. CA-removal is Off, Noise-reduction 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 24mm f1.8 compared to the Nikon Z 24mm f1.8 S. The Z-Nikkor was shot at a different day – but with roughly comparably atmospheric conditions. As the Viltrox was quite decentered I chose the better corner for this test. This might overstate the image quality of a perfectly centered copy of this lens.
You can access the large originals but please respect our copyright and only use those images for personal use.
Again the Viltrox AF 24mm f1.8 shows good sharpness in the center and a surprising amount of detail in the FF/FX-corner. But the area around the APS-C/DX-corner is soft and stays so until the lens is stopped down to f5.6. The Nikon Z 24mm f1.8 S in comparison is right sharp from the beginning across the full-frame sensor.
After looking at both sets of test images and the MTF chart it becomes clear that the weak spot of the Viltrox AF 24mm f1.8 is the area around 8-16mm image height where it is relatively soft and does not respond too quickly to stopping down. So for a good sharp landscape or architecture shot you should stop the lens down to f5.6 or even f8.0.
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 24mm f1.8 at different apertures. All images were developed from RAW to the same brightness in the center.
The sample images above show that even with vignette control applied vignetting of the Viltrox is pretty strong 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. Btw: JPGs straight out of camera showed less vignetting than the RAW files – which is the first time I’ve seen this effect. So something is off with the application of the integrated lens profile. Switching to the lens profile supplied with Adobe’s RAW-converter (which is for the E-mount version) lifts the corners much stronger (even stronger than with SOOC JPGs). The results are quite good when used on RAWs with vignette control switched Off in camera but overcompensate when vignette control was On. In this case reduce the amount of vignetting correction from Adobe’s lens profile to 50%.
Regarding distortions: Adobe’s RAW converter ignores what was set in camera and always corrects them. Still some of the complex pin-cushion plus mustachio distortions remain not fully corrected – even if you dial up the distortion correction in Adobe’s lens profile to 167%. There’s also a lens profile (only for the E-mount version) 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.
It does not look like a strong effect from using the lens profile in CRAW in the example above. But the closer you focus the more extreme the pin-cushion distortions become: Have a look at the sample image of a bookshelf below. In this case switching Adobe’s lens profile on and increase distortion correction to 200% (!) does make a huge difference.
Now, this is all a fine mess if you use the Viltrox AF 24mm f1.8 and want optimally corrected results. I personally would hesitate to switch vignette control or distortion compensation in my camera each time I swap lenses: You’re bound to forget this in the heat of a photo-shooting. I’d rather leave everything in camera at my usual settings and then apply the Adobe lens-profile in post-processing.
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 24mm f1.8 shows quite some coma at f1.8 and f2.0. But it’s much reduced at f2.8. Looking at the large original there’s also a bit of blue halo around street lights in the center at f1.8. But the effect is already gone at f2.0.
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 on 24mm f1.8 lenses Bokeh balls are always disappointingly small – and thus Bokeh is never a strong feature of wide-angle lenses. But the “beauty” of the balls is still important. Unfortunately the Viltrox is plagued by nasty onion-rings and strong outlining tinted green. This is indicative of a pretty busy background Bokeh possibly with double contours. Compression of the circle towards the corners is not that pronounced although the effect already starts in the APS-C/DX-corner at f1.8. But at f2.8 this is practically a non-issue. The aperture blades of the Viltrox are not well-rounded and show up already at f1.8 as they protrude into the path of light even wide open.
Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf. Again, the crops of the foreground, the middle-ground, and the background below the main image are resized to make them comparable across all my reviews.
Both the Viltrox and the Nikon he Viltrox manage to balance foreground and background Bokeh nicely with only little nervousness and a smooth transition in the middle-ground – albeit with a slightly stronger greenish cast from the Viltrox.
Below is another crop (now at 100%) from the same images showing the ruler. Except for the differences in perspective both lenses again look similar in the transition zone near the plane of focus.
But looking at some of the images on the next page you’ll find examples of double-contours in the background farther behind the plane of focus:
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 Viltrox AF 24mm f1.8 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:
The Viltrox does produce some flare, glare and ghosting but the images still keep a good level of black outside the immediately affected areas. And you should try to avoid the sun just outside the corners of the full frame as it induces a nasty streak.
The Viltrox AF 24mm f1.8 does not produce very well defined and regular sunstars: f8 is perhaps the best aperture:
Next check out my sample images!Check prices on the Viltrox AF 24mm f1.8 at B&H or Adorama. Alternatively get yourself a copy of my In Camera book, an official Cameralabs T-shirt or mug, or treat me to a coffee! Thanks!