I'm trying to use the Pi Camera as an affordable microscopy solution. So I'm taking pictures using raspistill directly through the imaging tube of my stereoscope and while the picture is of good quality, it has this strange uneven "illumination" artefact in the middle (see example):
I understand that the pink hue is due to some auto white-balance (I've tried them all, didn't go for the manual one yet tough. What, I don't understand is why this central part is more illuminated. I've reduced all gains to their minimum, and the illumination is very homogeneous in the scope itself.
I've also tried to acquire the same image using an olympus reflex camera, which gives perfectly normal results.
Any suggestions anyone? There are just so many parameters in raspistill