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Distortion
On the Z50, the lens takes advantage of the reduced size of the DX sensor and produces a small amount of barrel distortion at around 0.4%. With optional in-camera software correction enabled, distortion is reduced to around 0.16%.
Vignetting
Regarding vignetting, the lens again profits from the smaller DX sensor size. Wide open, the lens shows a native vignetting of around 3/4 of a stop wide open. As usual, stopping down reduces vignetting significantly, bringing the amount of light fall-off towards the borders down to around 0.2 stops from f/2.8 onwards.
Nikon offers in-camera correction for vignetting, which can be set to either 'off', 'low', 'normal' or 'high' in the camera menu, where the default setting is 'normal'. With that amount of 'normal' correction applied, around half a stop of vignetting remains at f/1.8, while from f/2.8 onwards it's reduced to a level that should not be noticeable anymore with most subjects.For JPGs, the chosen setting is applied to the final image.
If you shoot RAW, the selected setting is stored in the meta data to be applied later by the processing software. In addition, Nikon embeds the full lens correction profile into the NEF files. Surprisingly, none of the in-camera correction settings Nikon offers makes full use of the correction profile in the same way. Even at the 'high' setting, vignetting is not fully corrected.
If you shoot NEFs and use a RAW converter that allows full access to the embedded correction profile (like C1 does, for example, while Adobe products currently do not), vignetting can be completely eliminated.
MTF (resolution)
The Nikkor shows outstanding performance in the lab. On the Z50, the resolution is excellent across the whole frame straight from the maximum aperture and stays on this outstanding level down to f/5.6. From f/8 onwards, diffraction reduces the resolution figures to lower levels, but even stopped down to f/11 the results are still very good.
The lens showed a small amount of focus shifting when stopping down (residual spherical aberration).
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths
per picture height (LW/PH) which can be taken as a measure for sharpness.
If you want to know more about the MTF50 figures you may check out the corresponding
Imatest Explanations
Chromatic Aberrations (CAs)
Chromatic aberrations (color shadows at harsh contrast transitions) are very well controlled by the lens, with values of just below 0.3 pixels at the image borders wide open, slowly decreasing to completely unnoticeable amounts stopped down to f/11.
Bokeh
One of the main reasons to use a fast prime over any kind of slower zoom is its ability to separate the main subject from the background. For such images, the quality of the background blur is of major importance.
The Nikkor delivers very smooth and pleasing image blur in these kinds of shots.
Out-of-focus highlights are evenly filled with virtually no outlining. Thanks to the 9 rounded aperture blades, highlights retain their circular shape even when the lens is stopped down.
The shape of the highlights deteriorates a bit towards the image borders due to mechanical vignetting at large apertures, naturally to a lower degree than on a FX camera, though. However, stopping down solves that issue.
In the focus transition zone, the lens shows smooth image blur behind the focal plane (to the left below), but a bit more nervous bokeh due to mild double images in the foreground (to the right below).
Bokeh Fringing / LoCA
Bokeh fringing (non-coinciding focal planes of the various colors, also referred to as longitudinal chromatic aberration, or LoCA for short) is an axial color fringing effect and a common issue with relatively fast glass. The halos typically have different colors - magenta (red + blue) in front of the focus point and green beyond. Unlike lateral CAs, bokeh fringing can not easily be fixed in post processing.
The Nikkor is not free of of bokeh fringing, but shows a fairly low amount wide open for its lens class. As usual, stopping down the lens reduces the amount of bokeh fringing further.
In addition, these shots also illustrate the small amount of focus shift when stopping down that was mentioned in the MTF section. It's worth mentioning though that down to f/5.6, Z cameras focus with the lens stopped down (unless the lens is even slower than f/5.6, of course), so the focus shift can only become an issue if the lens is focussed manually and the aperture changed later (that's actually what we do for the images below).
Sample Shots
You can find some sample images taken with the Nikon Z7 in our FX review of the lens.
Verdict
The Nikkor Z 50mm f/1.8 S impressed us on the Z7 FX camera already, so the expectations of how the lens would perform on the smaller DX sensor of the Z50 were quite high. The lens did not disappoint, though: it delivers extremely sharp images across the whole DX frame, combined with very pleasing background blur.
The lens resolution is outstanding both because of the high level across the whole image frame straight from the maximum aperture, but also because of its uniformity across the tested aperture range (until diffraction kicks in and reduces the maximum possible resolution at smaller apertures).
Background blur is very soft and smooth with evenly filled highlights without visible outlining. The latter is also partly because of the fairly low amount of bokeh fringing. In summary, the bokeh quality is outstanding for this lens class.
CAs are very well controlled and no issue at all. Distortion is fairly low natively already and well handled by software correction, if applied.
Vignetting is not very pronounced thanks to the smaller area of the DX sensor. Software correction can take care of it completely, it's surprising though that Nikon does not make full use of its own correction profile in-camera.
The build quality of the lens is on a very high level. There are some plastic parts on the lens body, but most of it is made from aluminum and feels sturdy and solid. Controls on the lens are reduced to a minimum, just the AF/M switch and the focus ring. The latter works electronically thugh with variable speed and can be customized to control a (small) selection of other functions.
Thanks to a stepping motor, autofocus is very fast and silent.
So, in summary, a really impressive lens on the Z50 that easily deserves both our 'Highly Recommended' badge as well as the highest star rating.
Mechanical Quality:
★★★★★
Click here for an explanation of our star ratings
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