[popo]

[quote name='Brightcolours' timestamp='1291420436' post='4748']

I tried it with my 35mm f2 on my 450D.



In M, with the lens being "unknown" the images are a little bit darker than with the lens known, wide open with f2. Oddly enough, when trying with live view the "known" shot is a bit darker than the shot where the lens is unknown. Go figure?

[/quote]

I just tried it myself with the same (450D, 35mm f/2) set to M mode (actual f/2 1/15s ISO100).



Put camera on tripod in front of my monitor, put up a grey background and focused to infinity. With lens connected normally the in camera histogram was slightly higher than with lens twisted. This was done twice to rule out any shot to shot variation. I repeated this in live view, same result as before. That is, with the lens connected normally it was slightly brighter histogram than twisted.



Just to rule it out, I did it again with fixed white balance as I think there might be a slight colour shift too. Didn't change results.







Example histograms from one of each.



Edit: Repeated the test at f/8 1s. Here the twisted shots were fractionally brighter than the normally connected ones, but by a much smaller degree than above. It was repeatable and not shot to shot variation. So this seems to confirm there is some aperture dependant effect going on.