Olympus M.Zuiko 12-50mm 1:3.5-6.3 EZ ED - Review / Test Report - Analysis
Lens Reviews -
Tuesday, 16 April 2013 15:46
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Technically distortion is a bit of a weak point of MFT lenses because the system relies on an auto-correction and as such minimizing the issue isn't really a design priority. You may argue, of course, that this is not relevant from a user perspective because all the applied corrections are done "under the hood". This is also something that we can confirm - standard JPEGs or conventionally converted RAW files don't show a significant amounts of distortion. At 12mm, there is a moderate barrel distortion (1.9%) and it's negligible beyond.
However, it is still interesting to look a bit behind the scenes by using an "unsupported" RAW converter. Thi reveals the native barrel distortion level of a whopping 6.9% (!) at 12mm which is on the extreme side. At 25mm and 50mm it isn't overly relevant though.
Unsurprisingly the M.Zuiko produces some light falloff at 12mm at f/3.5 (~0.8EV). However, the issue isn't all that bad and stopping down reduces it to a moderate degree. There is nothing to worry about in the mid to upper focal length range.
The Olympus lens can't fully convince in terms of resolution. The center quality is very good at 12mm straight from f/3.5 and the borders are also pretty decent whereas the corners are slightly soft. Since the lens is quite slow, it basically runs immediately into diffraction effects so stopping down has only a slightly positive effect on the outer image region whereas the center quality decreases. The corner quality improves in the middle portion of the zoom range which is also the sweet spot of the lens. At 50mm there is quite a bit of a decrease in center performance although the quality is at least very even across the frame here.
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
Chromatic Aberrations (CAs)
Lateral CAs (colors shadows at hard contrast transitions at the image borders) are a bit of a weak spot. We measure the CA pixel width at the borders and at 12mm the issues isn't all that bad here (~1.3px). However, the CAs increase
significantly in the extreme corners to around 2.2px. The issue isn't quite as pronounced in the middle and upper focal length range.