Quality

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 Nikon Z 28mm f2.8 shows a bit of magenta in the foreground at f2.8 and f4.0. And there’s also some focus shift which makes the foreground less sharp when stopped down to f4.0.

Nikon Z 28mm f2.8 longitudinal Chromatic Aberration (loCA)

Above: f2.8 (top), f4.0 (bottom); 100% crops, left = foreground, right = background

In the following real life shot you can see some blue/purple fringing around high-contrast edges and bleeding of bright light into the shadows:

Above: Nikon Z 28mm f2.8 at f2.8; 100% crop, click image for 4k version, here for large original

Sharpness and contrast

Let’s have a look at the theoretical performance of the Nikon Z 28mm f2.8 first and compare it to the 24mm and 35mm alternatives from Nikon’s Z line-up:

Above: Nikon Z 28mm f2.8

Above: Nikon Z 24mm f1.8 S (left), Nikon Z 35mm f1.8 S (right)

These MTF charts show the computed lens-performance of lenses wide open at infinity without influence of diffraction at 10 line-pairs/mm (red) and 30 lp/mm (blue). 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 (DX-corner), and 20 mm (FX-corner) on a 45MP Nikon Z7 camera.

From the MTF-chart the new Z-Nikkor should be quite sharp inside the DX image-circle – almost comparable to the Z 35mm f1.8 S albeit with more astigmatism. Keep in mind though that the S-line Nikkors are shown at f1.8 while the Z 28mm f2.8 is shown at a much less challenging aperture of f2.8. Towards the FX corner overall contrast drops stronger than with the S-line lenses but the Z 28mm f1.8 still retains quite some detail.

Let’s see how this theoretical performance translates into real life results in the sharpness test based on Siemens-stars. Shooting distance was 45x focal length i.e. at around 1.3m. Processing was done in Lightroom 10.4/CRAW 13.4 from RAW to Adobe Color profile with the built-in lens profile compensating CA, vignetting, and distortions. 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 28mm f2.8 from f2.8 down to f11 compared to the Nikon Z 24mm f1.8 S and Z 35mm f1.8 S at f2.8.

Nikon Z 28mm f2.8 compared; 100% crop from center, DX-corner, FX-corner

Above: Nikon Z 28mm f2.8 at f2.8

Above: Nikon Z 24mm f1.8 S at f2.8

Above: Nikon Z 35mm f1.8 S at f2.8

Above: Nikon Z 28mm f2.8 at f4.0

Above: Nikon Z 28mm f2.8 at f5.6; also available at f8.0, f11

Wide open Nikon’s Z 28mm f2.8 shows solid performance. But compared to its S-line siblings it renders the center and DX-corner with less acuity and has the least contrast of the three lenses in the FX-corner. Stopping the Z 28mm f2.8 down to f4.0 visibly improves sharpness in the center and contrast in the FX-corner. The test also showed the Z 28mm f2.8 to have pretty strong field-curvature while the Z 24mm f1.8 S and Z 35mm f1.8 S are practically free of it.

Performance at long distances

As performance of lenses also depends on the shooting distance I present another series of test-shots of a city around 1 km away. Processing was done in Lightroom 10.4/CRAW 13.4 from RAW to Adobe Color profile with the built-in lens profile compensating CA, vignetting, and distortions. 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.

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, DX-corner, and FX-corner from the Nikon Z 28mm f2.8 compared to the Nikon Z 24mm f1.8 S and Z 35mm f1.8 S at f2.8. The latter were shot at different days but atmospheric conditions were pretty comparable. 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.

Above: Nikon Z 28mm f2.8 at f2.8

Above: Nikon Z 28mm f2.8 at f2.8; 100% crops, click image for 4k version, here for large original

Above: Nikon Z 24mm f1.8 S at f2.8; 100% crops, click image for 4k version, here for large original

Above: Nikon Z 35mm f1.8 S at f2.8; 100% crops, click image for 4k version, here for large original

Above: Nikon Z 28mm f2.8 at f4.0

Above: Nikon Z 28mm f2.8 at f5.6; also available at f8.0, f11

Contrast is a bit muted on the Nikon Z 28mm f2.8 wide open and profits visibly from stopping down to f4.0 where it can almost keep up with its S-line siblings. The FX corner suffers from strong vignetting until stopped down to f5.6 .

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 three shots each with the new Z-Nikkor from f2.8 to f5.6 and focused to infinity. All images were developed to the same brightness in the center and are shown with vignette control Off (1st row) resp. Normal (2nd row):

Above: Nikon Z 28mm f2.8 on a full-frame (FX) camera without vignette control (top) / vignette control set to Normal (bottom)

The sample images above show that even with the lens profile applied vignetting is very visible at f2.8. But from f4.0 onwards light fall-off is OK. At f2.8 vignette control lifts the extreme corners about 0.5 EV which is pretty moderate. Set Vignette control to “high” to give the corners a stronger lift.

On a DX camera like the Nikon Z fc or Nikon Z 50, vignetting is much less of a problem:

Above: Nikon Z 28mm f2.8 on a cropped sensor (DX) camera without vignette control (top) / vignette control set to Normal (bottom)

Adobe’s RAW converter automatically applies Vignette control as it was set in camera – but you cannot alter the setting in postprocessing. With distortions you even cannot change the setting in camera: it is always (well) corrected by the lens profile:

Distortions: Nikon Z 28mm f2.8 with auto distortion control On

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 of the Nikon Z 28mm f2.8 at different apertures:

Above: Nikon Z 28mm f2.8 at f2.8; click image for 4k version, here for large original

Above: Nikon Z 28mm f2.8; 100% crops from the FX-corner at f2.8 (left), f4.0 (middle), f5.6 (right)

The Nikon Z 28mm f2.8 produces very visible coma in the FX-corner wide open. But stopping down to f4.0 reduces the problem considerably. Coma is also much less of a problem in the DX image-circle even at f2.8.

Bokeh quality

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, DX-corner, and FX-corner resized to make them comparable across all my reviews.

Above: Nikon Z 28mm f2.8 at f2.8; click image for 4k version

Above: Nikon Z 28mm f2.8 at f2.8; click image for 100% crop

Above: Nikon Z 28mm f2.8 at f4.0; click image for 100% crop

Above: Nikon Z 28mm f2.8 at f5.6; click image for 100% crop

The diameter of the Bokeh balls in the center is determined by the entrance pupil of the lens which is only 10mm. So it’s no surprise that the Z-Nikkor produces very small Bokeh balls. There’s also strong outlining with a bit of coloration and some weak onion rings. Stopping down to f4.0 already produces non-circular Bokeh balls.

Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf. Crops are from the foreground, middle-ground, and background resized to make them comparable across all my reviews.

Above: Nikon Z 28mm f2.8 at f2.8

Above: Nikon Z 28mm f2.8 at f2.8; click image for 4k version, here for large original

Above: Nikon Z 24mm f1.8 S at f1.8; click image for 4k version, here for large original

Above: Nikon Z 35mm f1.8 S at f1.8; click image for 4k version, here for large original

The Nikon Z 28mm f2.8 has the least attractive Bokeh of the three lenses due to its slow focal ratio. Especially the foreground looks nervous but other than that Bokeh is not bad for a 28mm f2.8 lens.

Looking at another crop (now at 100%) from the same images showing the ruler reveals the Nikon Z 28mm f2.8 renders a relatively soft transition zone devoid of double contours which especially the Z 35mm f1.8 S shows prominently.

Above: Nikon Z 28mm f2.8 at f2.8; click image for 4k version, here for large original

Above: Nikon Z 24mm f1.8 S at f1.8; click image for 4k version, here for large original

Above: Nikon Z 35mm f1.8 S at f1.8; click image for 4k version, here for large original

Close-up performance

The Nikon Z 28mm f2.8 goes down to around 1:5 magnification. The following images were shot at 1:5.2 magnification where the area of sharp focus is just 125 x 187mm. The 100% crops shown below are from 0mm, 12mm, and 18mm off the center of the sensor respectively. For the following crops I focused once on the center wide open and did not change focus: Each row of crops is from the same shot, focused optimally for the center. So this is the best results you can get from a single shot as any issues with field curvature show up here.

Nikon Z 28mm f2.8; 100% crop from center, DX-corner, FX-corner

Above: Nikon Z 28mm f2.8 at f2.8, 1:5.2

Above: Nikon Z 28mm f2.8 at f5.6, 1:5.2

Above: Nikon Z 28mm f2.8 at f11, 1:5.2

Results at f2.8 are soft and suffer from reduced contrast even in the center. Better to stop the Nikon Z 28mm f2.8 down to f5.6 which raises contrast and sharpness considerably – especially in the DX image circle. Stop further down to give the outer image area another lift in acuity.

Flare, 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 Nikon’s Z 28mm f2.8 for these artifacts I went through a series of well calculated shots against a strong light-source to provoke glare and ghosting. Following are two 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:

Above: Glare and ghosting from strong light hitting the Nikon Z 28mm f2.8 at f2.8; click image for 4k version or here for +3 EV exposure compensation

Above: Flare from strong light hitting the Nikon Z 28mm f2.8 at f11; click image for 4k version or here for +3 EV exposure compensation

The Nikon Z 28mm f2.8 produces some weak ghosting artifacts and the blacks stay pretty black even in adverse contra light situations.

The lens starts producing sunstars already at f4.0 due to the less than perfectly circular aperture opening:

Above: Sunstars from the Nikon Z 28mm f2.8 at f4.0, f5.6, f8.0 (from left to right), 100% crops

Next check out my sample images!