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 new Nikon is no exception: it shows quite some loCA at f1.8 and f2.8.
The test also revealed that there is no focus shift to speak of at distances of 1m and farther away. For comparison have a look at the Nikon 24mm f1.8G, Nikon 24mm f1.4G, and Sigma 24mm f1.4 Art. Even the apochromatic Zeiss Otus 28mm f1.4 shows some loCAs (all f1.4 lenses shown at f1.4/f2.0/f2.8).
The following real life shot shows that the Nikon Z 24mm f1.8 S produces only little purple fringing around high-contrast edges in the focal plane or green outlining around background subjects:
Sharpness and contrast
Let’s have a look at the theoretical performance of the new Nikon Z 24mm f1.8 S first and compare it to the performance of the Nikon 24mm f1.8G and two f1.4 alternatives from Sigma and Nikon:
These MTF charts show the computed lens-performance wide open 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/DX-corner), and 20 mm (FF/FX-corner) on a 45MP Nikon Z7 body.
From the charts the new Nikon Z 24mm f1.8 S should have a clear advantage over the Nikon 24mm f1.8G. The older F-Nikkor has a distinct drop in resolution of fine details at 10mm image height and then again towards the extreme corner of a full-frame sensor. Both f1.4 lenses look even worse, but keep in mind that their MTF-values are shown at f1.4 which gives them a 2/3 of a stop disadvantage.
Let’s see how this theoretical performance of Nikon’s new Z Nikkor 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.
The following 100% crops show the Nikon Z 24mm f1.8 S from f1.8 down to f11 compared to the Nikon 24mm f1.8G, Nikon 24mm f1.4G, Sigma 24mm f1.4 Art, and Zeiss Otus 28mm f1.4 at f2.0 plus the Nikon Z 24-70mm f2.8 S at f2.8. The F-Nikkors and the Sigma were shot on a D810 whose linear resolution is 11% lower than from the 45MP Z7. This should give these older lenses a slight advantage in this comparison but you still can get a good idea how they perform. No lens profiles were applied to the Zeiss, Sigma, and F-Nikkor lenses.
At f2.0 the Nikon Z 24mm f1.8 S does not leap ahead of the older lenses. It does show a very good overall contrast right up into the FX-corner but resolution of fine details there is not the best. It even falls behind the Nikon 24mm f1.8G in that respect although the older lens covers the detail in a veil of coma. The reference Otus lens sets the performance bar again in this comparison.
Let’s compare the new Z Nikkor to the Nikon Z 24-70mm f2.8 S at f2.8:
At f2.8 it’s pretty close but the Nikon Z 24mm f1.8 S falls a bit behind the zoom lens at the DX-corner.
Now let’s see how the new Z Nikkor develops when stopped further down:
Stopping down to f4.0 or f5.6 gives the acuity of the lens a further lift bringing performance at the corners closer to the very good center. Btw.: The Nikon Z 24mm f1.8 S shows no field curvature, all crops are from the same shot.
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 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 64 and VR switched off. As usual I have selected the diagonal that provided the better corner results as the Nikon Z 24mm f1.8 S was a bit decentered.
The main image shows the complete scene wide open to give you an impression of the angle of view and to judge vignetting of the Nikon Z 24mm f1.8 S. 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 center, DX-corner, and FX-corner down to f11 compared to the Zeiss Otus 28mm f1.4 at f2.0 and the Nikon Z 24-70mm f2.8S at 24mm, f2.8. The Otus and the zoom were shot at other days but under similar atmospheric conditions. The Zeiss Otus is a bit advantaged in this comparison as due to its 17% longer focal length it has a higher magnification of the scene. No lens profile was applied to the Zeiss Otus.
You can click on each image to access the large original. Please respect our copyright and only use those images for personal use.
At f2.0 the Nikon Z 24mm f1.8 S looks at least as sharp as the Zeiss Otus. Impressive! Let’s compare the new Z Nikkor against the Nikon Z 24-70mm f2.8 S at 24mm, f2.8:
Putting differences in overall contrast aside which might stem from different humidity in the air the Nikon Z 24mm f1.8 S seems to have a slight advantage in resolution over the Nikon Z 24-70mm f2.8 S.
This is how the new Z Nikkor develops when stopped further down:
The Nikon Z 24mm f1.8 S renders the center very sharp already at f1.8 with only slight softening toward the corners. And at f4.0 the lens is very sharp across the frame. The results from the long-distance test seem to indicate that the Nikon Z 24mm f1.8 S performs a bit better in the distance than up close. Some of the sample images support that too.
Vignetting and distortions
With Nikon’s Z cameras you can select the degree of Vignette Control in camera between High, Normal, Low, and Off. Sadly Adobe’s RAW converter ignores all lens profile settings and treats them as if they are set to Normal/On while Nikon’s Capture NX-D software allows to change the settings when developing RAWs.
To make it easier to see light fall-off in the corners of a full-frame sensor I’ve arranged a series of three shots with the Nikon Z 24mm f1.8 S at different apertures. All images were developed to the same brightness in the center and the lens profile applied, Vignette Control in camera was set to Normal (the default). This lifts the extreme corners by about 2/3 EV at f1.8:
The sample images above show that even with the lens profile applied vignetting remains very visible at f1.8. See the Zeiss 28mm f1.4 Otus with the Adobe lens profile applied in comparison:
Adobe goes for a much stronger vignette compensation with the Zeiss Otus than Nikon does with its Z Nikkor.
Regarding distortions: The new Z 24mm f1.8 S is very well corrected through Nikon’s lens profile as you can see in the examples at the end of the samples page.
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 FX-corner at various apertures:
The Nikon Z 24mm f1.8 S has very little coma wide open, even less than the already very good Zeiss 28mm f1.4 Otus.
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.
The 44% crops below the main image show the Bokeh balls at the center, DX-corner, and FX-corner at the largest aperture:
When shot wide open the Z 24mm f1.8 S shows only a moderate cat’s eye effect toward the FX-corner. There are some mild onion rings and also some green outlining due to longitudinal CAs.
Let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf compared to the Zeiss Otus 28mm f1.4.
Despite the Zeiss Otus having an f1.4 focal ratio it cannot pull clearly ahead of the Nikon Z 24mm f1.8 S. Nikon’s new lens manages to balance foreground and background Bokeh nicely with only little nervousness and a smooth transition in the middle-ground.
The Nikon Z 24mm f1.8 S goes down to 1:5.7 magnification with manual focusing. Its performance is very usable once you stop down to f5.6. The following image was shot at 1:5.9 magnification where the area of sharp focus is just 142 x 212mm. The crops shown below are from 2mm, 13mm, and 20mm off the center of the sensor respectively:
This seems a little softer than e.g. the Z 50mm f1.8 S can do – which also has the benefit of a much longer working distance.
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 new Nikon Z 24mm f1.8 S for these artefacts 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. See an examples at f11 where these effects normally show up most prominently. 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 Nikon Z 24mm f1.8 S is very clear of flare and ghosting artefacts. And outside these artefacts the new lens renders a very deep black, so there’s little veiling glare. The lens also does not produce the typical flare which other lenses show when the light-source is just outside the corner.
All-in-all the Nikon Z 24mm f1.8 S let’s you shoot confidently under adverse contra-light situations. The only drawback being that the Z7 might add some colorful “teardrops” to very bright sunstars as can be seen above. The effect can not always be seen though as the examples below show. To produce nice sunstars the Nikon Z 24mm f1.8 S needs to be stopped down to 5.6:
Next check out my sample images!Check prices on the Nikon Z 24mm f1.8 S at Amazon, B&H, Adorama, or Wex. Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!