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Tokina RMC 17mm f/3.5 - Review / Lab Test Report - Analysis |
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Lens Reviews -
Pentax
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Page 2 of 2
Distortions
The Tokina exhibits a fairly pronounced degree of barrel distortions (~2.5%). This isn't bad
for a lens in the focal length class and it is nothing special either.
The chart above has a real-world size of about 120x80cm.
Vignetting
As mentioned the Tokina is a full format lens so it has a sweet-spot advantage when used on
an APS-C DSLR. However, at f/3.5 the amount of vignetting is still fairly heavy (~1.14EV).
Stopping down to f/5.6 and beyond reduces the problem to a manageable degree.
MTF (resolution)
The Tokina was able to surprise with a pretty decent resolution characteristic in the
MTF lab. At f/3.5 the center and border is already on a very good level whereas the
extreme corners are quite soft. Stopping down increases the quality and the peak
performance is reached at f/8 with an excellent center resolution and very good
borders and extreme corners. The Tokina can also keep this level at f/11 without any
big impact from diffraction effects.
While this sound pretty good it is also worth to mention that the contrast level is
very low at f/3.5. I'd say that the color rendition is also a bit off the
mainstream.
The lab-type tests did not show any significant problems
but some field shots (infinity focus) showed a rather pronounced softness on the left
hand side of the image field so the age of the lens obviously took its toll somewhere.
Below is a simplified summary of the formal findings. The chart shows in line widths
per picture height (LW/PH) which can be taken as a measure for sharpness.
The chart is limited to the visually relevant LW/PH range of [850, 2350].
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 a
significant problem at large aperture settings - at f/3.5 and f/5.6 the CAs
reach an average width up to ~2px at the image borders. At f/8 and f/11 the
problem is reduced and not overly disturbing anymore.
Verdict
The Tokina RMC 17mm f/3.5 may be an oldie but it is still a fairly high
resolution lens especially when stopped down a bit. At f/3.5 the contrast
level is very low and the amount of vignetting is quite pronounced
so it is a good idea to avoid this setting. The lens shows a high
degree of barrel distortions but if we put this into context this is a
quite normal behavior in this focal length class. The build quality is
exceptional but using such an old lens on the Pentax K10D is a bit
cumbersome. The Tokina had its time but frankly the Pentax DA 16-45mm f/4 ED AL
(for instance) is a better choice.
| Optical Quality: |  |
| Mechanical Quality: |  |
| Price/Performance: | discontinued |
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