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Nikkor AF 20mm f/2.8 D - Review / Test Report - Analysis |
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Lens Reviews -
Nikon / Nikkor (APS-C)
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Page 2 of 2
Distortion
The AF 20mm f/2D exhibits a very pronounced degree (2.3%) of barrel distortion
which can be quite noticeable in real-world scenes. This is a little disappointing
for a fix-focal because it does not perform any better than an average APS-C
standard zoom here.
The chart above has a real-world size of about 120x80cm.
Vignetting
The AF 20mm f/2.8 D is a full frame lens thus enjoying a sweet spot advantage
on APS-C DSLRs. Nonetheless the vignetting at wide-open aperture is very
high at 1.36EV which will be noticeable in some situations. From f/4 and up
the problem is well controlled for a (native) ultra-wide lens though.
MTF (resolution)
The Nikkor didn't really convince in the resolution tests. The center performance
is very good to excellent and the borders follow closely. However, the extreme
corners fall apart in quality reaching only good figures at medium aperture
settings. It's interesting that the Canon EF 20mm f/2.8 USM showed a similar
behavior though to a lesser degree (better extreme corners). In both cases this is a
bit disappointing especially when taking the full frame design into account - seems
as if the projection characteristic of these legacy lenses isn't really perfect for today's
image sensors which prefer a perpendicular path of rays. The performance of the tested
sample was very symmetrical so it didn't seem to be a bad sample.
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 pretty
bad especially for a fix-focal. With an average CA width of around 2x at the
image borders the Nikkor is among the worst fix-focals tested so far.
Verdict
The Nikkor AF 20mm f/2.8 D had a very good reputation during the film era but
the D200 didn't really like the lens. The resolution is fine for most of the
APS-C image frame but the extreme corners never really reach impressive results
even at medium aperture settings. Vignetting is fairly high at f/2.8 and CAs
are pretty bad. All-in-all you may prefer to look elsewhere to cover this focal
length on an APS-C DSLR.
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