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Tamron AF 14mm f/2.8 SP Aspherical [IF] (Pentax K) - Review / Lab Test Report - Analysis |
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Lens Reviews -
Pentax
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Page 2 of 2
Distortion
Ultra-wide lenses are very difficult to correct and a focal length of 14mm is
fairly extreme for a full format lens. As such it is not surprising that the Tamron shows a
quite significant degree of barrel distortion (2.5%). However, even so this is still
better than many ultra-wide zoom lenses.
The chart above has a real-world size of about 120x80cm.
Vignetting
The Tamron AF 14mm f/2.8 SP may be a full format lens but it still suffers from a
fairly hefty degree of vignetting (1.4EV @ f/2.8) when used on the K10D - surely
a side effect of the comparatively fast max. aperture. The situation is already
much better at f/4 and vignetting should be fairly negligible under field conditions
from f/5.6 onwards.
Here's an example shot taken @ f/2.8:
MTF (resolution)
The Tamron produced rather mixed resolution results in the lab. The center
performance is superb straight from the max. aperture. However, the borders
and more so the extreme corners aren't quite as impressive especially
at f/2.8 where the word "soft" comes into mind. At f/5.6 the results are
very good although not any better than the quality delivered by modern zoom
lenses in this range. At f/11 diffraction effects results in the usual decrease
of quality. The field curvature is relatively moderate for an ultra-wide lens.
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)
Lateral chromatic aberrations (color shadows at harsh contrast transitions) are
comparatively low at large aperture settings but increase significantly
when stopping down. At f/8 to f/11 CAs reach a rather disturbing degree of
1.8-2px on the average at the image borders.
(Note: CAs can be reduced via imaging tools)
Verdict
The Tamron AF 14mm f/2.8 SP Aspherical [IF] is a slightly disappointing
performer on the K10D - a fate that it shares with the quite similar
Nikkor AF 14mm f/2.8D ED on Nikon DSLRs. It seems as if these fairly old
ultra-wide fix-focal lenses aren't the best match for today's DSLRs
anymore. The center resolution is nothing short of superb but the border
and extreme corner quality, and this is important in this class, is not
quite as impressive specifically at large apertures. The level of barrel
distortions is quite good for a lens in this class whereas CAs (color shadows)
are on the high side. Vignetting is a problem at f/2.8 but fairly well
controlled beyond. The build quality is pretty decent. So is the Tamron
worth the high price (~1100€/US$) ? The Tamron shines regarding its
large max. aperture but quality-wise it doesn't offer anything beyond
the mainstream. If you're looking for a "duo-mode" (film + digital) lens
the more affordable Sigma AF 12-24mm f/4.5-5.6 EX is at least as good
(although slower) and there're a couple of good alternatives among the
digital-only ultra-wide lenses.
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