Tokina RMC 17mm f/3.5 - Review / Lab Test Report - Analysis
Lens Reviews - Pentax
Article Index
Introduction
Analysis

Distortion

The Tokina exhibits a fairly pronounced degree of barrel distortion (~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 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 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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