Distortion

The MFT system applies auto-correction for distortion so its usually not an issue to worry about. The corrected images show less than 1% barrel (40mm) to pincushion (70mm+) distortion. The RAW (=uncorrected) data suggests a different characteristic - not really in the medium to long range but there's a strong degree (4%) of barrel distortion at 40mm.

Vignetting

MTF (resolution)

The M.Zuiko 40-150mm R may not be a high performance lens but it does a decent job in terms of resolution. At 40mm (f/4-11) the results are generally very good in the image center and good to very good in the outer image field. Moving out to 70mm, there's only a marginal decrease in quality and it is still fine at 100mm. The resolution is somewhat more reduced at 150mm with a good to very good center and good borders. The extreme corners are soft at f/5.6 so you should stop down to f/8 here - this is a good idea anyway in order to boost the contrast at this focal length.

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 strong transitions) are a bit of an issue at the wide end (40mm) of the zoom range where they vary between 1.3-1.8px on the average at the image borders. This can be visible in certain scenes. However, there's nothing to worry about at longer focal lengths.