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Pentax SMC DA* 60-250mm f/4 ED [IF] SDM - Review / Test Report - Analysis |
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Lens Reviews -
Pentax
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Page 2 of 3
Distortion
The Pentax lens produces only a moderate level of barrel distortion at 60mm and very slight pincushion distortion
beyond. This is not objectionable.
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Move the mouse cursor over the focal length text marks below to observe the respective distortion
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| 60mm |
135mm |
200mm |
250mm |
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The chart above has a real-world size of about 120x80cm.
Vignetting
Vignetting is very well controlled for a dedicated APS-C lens. At 60mm and 135mm it's barely
detectable even in lab conditions. At 200mm and 250mm f/4 it's getting a little stronger but
it shouldn't be an issue anymore if you stop down by 1/2 f-stop.
MTF (resolution)
(revised) The resolution characteristic of the Pentax lens is pretty harmonious throughout the range. At 60mm the center resolution is very good to excellent throughout the tested aperture range. The borders
are a bit weaker but still on a very good level even at f/4 (just). Moving towards the long end of the
range the center performance decreases marginally whereas the border quality remains very good. The
peak performance is located around the 135mm setting.
Following a bit of a Pentax tradition the tested sample wasn't perfectly centered specifically at 60mm where
the left side of the image field showed a slightly stronger performance than the right one. A perfect sample
should show better border results at 60mm a possibly a marginally higher center performance at f/4.
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 are generally well controlled specifically at 60mm and 135mm. The problem increases somewhat at 200mm & 250mm where the CA reach levels beyond 1px at the image borders - this may be visible at times but it doesn't reach an annoying degree.
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