In response to your

They do if they both have a lens of the same diameter focusing light on it.

That’s the thing. They are not the same diameter. I have an 85mm FF lens, front element is about 55mm across, a 14mm FF that’s about 75–80mm across. Even the ‘normal’ lens (50mm on FF) is 40mm across. These are all relatively fast primes, BTW.

MFT lenses are smaller and a lot lighter than FF (much more of a deal than the difference in weight between bodies). This is exactly why MFT is a great hiking system.

When I mentioned ‘a concentrator’ I was talking about the (AFAIK theoretical) advantages of using, say, a FF lens on an MFT system, and refracting all that incoming light onto the MFT sensor. But you’d then lose the weight advantage.

If you want to measure some of your MFT lenses, I’m talking about the width of the front element glass, not the shade or overall diameter (both of those lenses I mention are a good bit larger than their front elements, and the 14mm is stupid-heavy, something I regret every time I lug it to a dark site for astro).

Again, go head over to the photography tech forum on DPReview, tell those folks how very wrong they are — and you’ll get more explanation than I have energy to go into here.

Popping this back up to the main response section as Medium won’t let me respond there.