With some torrential rain showers now affecting us and being bored I made what I thought would be a pointless colour version of the day 22 entry from the raw file only to find I needed to correct for vignetting which I hadn't detected on the jpeg monochrome from the camera. It doesn't occur on another shot from the same position taken at a marginally longer focal length so perhaps it's due to the uv filter I've got on the lens, despite it being a thin one, bother! Still I was able to make a manual correction in the software.
Barrie
Update:-
I've just managed some test shots between hail showers and it's the lens and not the presence of the filter, there's some vignetting with the zoom at 12mm and aperture at f/3.5, didn't check what happens when you stop down but probably soon disappears, I know it wasn't there at a zoom setting of about 15mm wide open.