Hi, I have just seen this video and I think he is right. https://www.youtube.com/watch?v=DtDotqLx6nA If you are in a hurry, the part about aperture equivalence, IMO the most interesting, starts at 20:20. I'm not so convinced about the "marketing cheating" part: from one point of view they are giving a false information, but at the same time they are saying something most users can understand. It's quite borderline to me. Anyway I think it's a good thing to know to better understand why and how a 300mm 2.8 can be so small (it cannot) and so on. Just to be sure I got it right I took an adapted FF Nikon lens and an Oly native lens and I took the same shot with the same three exposure values and I got the same brightness in the two pictures. So, if the Nikon lens at 2.8 has twice the physical opening of the Oly at 2.8 where is the extra light gone? I suppose it just bounced against the adapter and on the area around the sensor and got reflected outside of the lens. But more light enters the lens and that's why I can use a speed booster to use that extra light. And this is also why I cannot use a speedbooster to boost a Oly lens from 2.8 to 1.4. Am I correct?