Hello all, I don't post often and I'm new on this forum and I need a little help. I got a good deal on a Lumix G5 for Christmas and I'm playing around with a few old MF lenses and adapters. Yesterday I figured out I'd compare two silver noses: Canon FD 50mm 1.4 against another oldie, the Olympus OM F.Zuiko 50mm 1.8. 1. I attached the camera to a tripod with the Canon lens at F1.4, iso 800, focused on an indoor scene, and got a reading of 1/50th of a second. 2. I then proceeded likewise, same scene, same iso, except I switched the Canon for the Olympus and set it to its minimum aperture of F1.8. Lighting conditions were exactly the same (indoor, no light from outside, ceiling lamp), and I got a reading of 1/40th. 3. By curiosity I switched lenses again and slid the aperture ring on the Canon down to the next click (between 1.4 and 2, most certainly 1.8). To my surprise I got the same value as when set to 1.4: 1/50th! Conclusions / Questions: a - Wide open, the difference in light transmission between the Canon at 1.4 and Oly at 1.8 is only 20% (1/50 to 1/40), shouldn't I be expecting a full stop (eg a difference more like 1/80th to 1/40th)? b - 1.4 and 1.8 give me the same shutter speed on the Canon: why?! Is the M4/3 adapter acting like a baffle that's limiting light transmission at the widest aperture? c - Since the Canon at 1.8 gives me 1/50th and the Oly at 1.8 gives me 1/40th, could it be that my Oly is underperforming at 1.8 (it does have very light fungus on several elements)? This would explain conclusion a. By the way I compared test pictures and they all seem evenly exposed so I'm not questioning the light meter on the camera. All your observations are warmly welcome! Many thanks.