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. It ranges from a moderate (~1.78%) barrel distortion at 14mm to marginal (0,06%) pincushion distortion at 140mm. This is nothing to worry about from a field perspective.
However, the non-corrected raw images show a pretty different situation with an extreme (~6.16%) barrel distortion at 14mm as well as slight (0.52%) barrel distortion at 140mm.

Vignetting

The 10x 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 ~1,1EV 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.

However, it's no surprise that the non-corrected (RAW) images show considerably worse results particularly at 140mm with a very heavy amount of vignetting of up to ~1.9EV at f/5.8 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 140mm from open aperture to f/11.

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

MTF (resolution)

The Panasonic lens produced quite decent resolution figures in the MTF lab and some shortcomings can be largely explained by its 10x zoom range. The center performance is generally very good in the wide- to medium range and it drops to good to very good levels beyond. The border quality is - unsurprisingly - worse but still good till about 70mm. However, you should avoid a large aperture settings at longer focal lengths if you want to catch details across the image frame.

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 this Panasonic 10x zoom. These color shadows are visible throughout the whole focal length with an average CA width of around ~0.7px at the image borders for auto-corrected and ~1.4px for non-corrected RAWS. The latter value can be disturbing on Olympus cameras where the RAWs are not auto-corrected. However, the best setting is at 14mm with only marginal lateral CAs.

The following figures show the corresponding performance of auto-corrected JPEGs obtained straight from the camera compared to non-corrected raw files.