Distortion

The image distortion produced by micro four-thirds images is auto-corrected either directly in the camera (JPEGs) or in most RAW-converters. The "exposed" distortion is therefore very moderate especially for an ultrazoom. They range from a moderate (~1.26%) barrel distortion at 14mm to marginal (0,15%) pincushion distortion at 150mm. This is nothing to worry about from a field perspective.
However, the non-corrected raw images show a pretty different situation with an extreme (~5.71%) barrel distortion at 14mm as well as moderate (1.21%) pincushion distortion at 50mm.

Vignetting

The "high-power 10.7x zoom" has a fairly mediocre vignetting characteristic. The following figures show the corresponding performance of auto-corrected JPEGs obtained straight from the camera compared to non-corrected raw files.

At 14mm and f/4 the amount of vignetting is very pronounced at ~0,9EV which is easily noticeable in field images. Nevertheless, the situation improves when stopping down to f/5.6 and it's not really an issue anymore from f/8 onwards. There is only a slight to marginal light falloff at longer focal lengths.

However, it's no surprise that the non-corrected (RAW) images show considerably worse results particularly at 14mm with a very heavy amount of vignetting of up to ~1.96EV at f/4 which is even beyond our normal scale for Four-Thirds tests. The following graphs compare the vignetting characteristic of auto- and non-corrected files between 14 and 150mm from open aperture to f/11.

The following images illustrate the above mentioned heavy vignetting at 14mm.

MTF (resolution)

The Olympus lens produced fairly average resolution figures in the MTF lab although it's pretty acceptable considering its huge focal length range. The center performance is generally very good at wider focal lengths and very good at tele settings. Te border quality is - unsurprisingly - worse but still good till about 50mm. However, you should avoid a large aperture settings at longer focal lengths if you want to catch details at the borders.

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 CAs (color shadows at harsh contrast transitions) are quite a weakness of the Olympus M.Zuiko. These color shadows are very pronounced throughout the whole focal length with an average CA width of around ~1.7px at the image borders and a maximum of ~3.4px at 90mm and f/5.6. This amount of CAs can be disturbing. The only really good setting is at 22mm. Unlike the Panasonic lenses the CAs are not auto-corrected neither by the camera nor by e.g. Photoshop. This is somewhat surprising because this is actually an easy and very desirable correction aspect.