12-60 vignette on E-5/EPL-1 but not E-1

Danielvr wrote:

Just shoot JPG for this purpose, or even simpler: see if the affected images are larger than the 4032 x 3024 pixels specified by Olympus. If they are, you should ignore the outer edges formed by the additional pixels when judging image quality.

Those extra pixels exist only to help properly demosaic and sharpen the actual image. Nearly all 3d party 'raw developers' rely on DCRAW source code to do the actual raw developing, and DCRAW tends to develop all available sensor data, including those edges that were never intended to be part of the final image.