More trivia re: Panasonic:
"Multi-aspect ratio Like the Panasonic LX3 compact camera the GH1 now uses a multi-aspect ratio sensor. At any aspect ratio (even at 4:3) it only uses a crop from the total available sensor surface which is slightly larger than a standard Four Thirds sensor in order to accomodate the different aspect ratios. At first sight this may seem strange but the result is that the
lens offers the same diagonal angle of view regardless of selected aspect ratio, making it much easier to get a feel for the behaviour of the lens. It also means you make the most of the sensor area, getting similar pixel counts in all modes."
https://www.dpreview.com/reviews/panasonicdmcgh1 ... scroll about halfway down ...