I'm using some SLR legacy lenses on a mirrorless camera that I have, and I am under the (subjective) impression that if the aperture is wide open, the colors are more vibrant, while closing the aperture a few stops down causes them to become dull and less saturated.
This is all anecdotal, since whenever I tried putting it to the test, I haven't been able to verify this. (By varying the shutter speed to retain the same ISO and exposure level)
I've discussed this with a friend, and while he has a similar impression, he can't explain it either; I haven't been able to find anything on the topic of aperture affecting color contrast anywhere.
Anybody that could confirm (or disprove) this theory? Since this is more of an impression, I don't expect it to be necessarily correct; I'm more interested in seeing if this is the common experience and whether there is something in the way lenses are constructed that would explains that, not in my particular case, but in general.
Setup: I'm using a canon fd 50mm 1.8, a Canon FD 135mm F/3.5 SC and a Pentax 50mm f/1.7 SMC-M on a MFT Mirrorless body. Simple adapters with no optics, no light leakage (tested with long exposure times in the dark and flashlight shining at the seams). No visible light source in/around the frame that would cause obvious flare — no filters, even though all these would reduce contrast, not increase constrast. I have a similar impression from using my native 14-42mm ez (3.5-5.6) lens: it feels as if it has much duller colors overall than the bright adapted lenses.