[JJ_SO]

First of all - this thing has to be compared to a 400mm f/5.6 L IS - not a 200mm f/2.8. If we agreed on that logic in the past we should stick to it regarding price comparisons as well.

Sorry, "we" didn't agree. Only that part of "us" who just loooooves to compute with DoF and equivalence the hell out of it - don't count me in, I strictly deny this single sided DoF only view. Fair enough for landscape stuff, not fair enough for sports or birds - here the only thing what counts is speed of a lens, defined by max. aperture.

 

The other part, who basically sees a fast lens and another fast lens - oh yes, and difficult noise situations from too small sensors - but a f/5.6 lens doesn't improve things much... at the end of the day you'd end up with a blurred FF shot, no matter what resolution the sensor brings, and the µ 4/3 will just be sharper because of a quarter of the shutter speed you'd need for f/5.6. The ISO game doesn't work too well. I still bet, that Leica lens will be more impressive wide open than a FF with a more than mediocre but cheaper 100-400 wide open at the long end. That's what primes do - declass zooms, at least the less costly ones.

 

Thus it is commendable that Panasonic made the effort but it's not more than a halo lens for showrooms in my opinion.

Here "we" agree But I just don't think, that somebody who wanted to go for mirrorless because of weight reductions will get a FF with a 100-400 for a reasonable price (cheaper than the 200mm Leica and as performing as it) plus carry that extra luggage around.

 

And don't forget: silent shutters are only available in mirrorless land - DSLRs just allow one shot, after that the bird is gone. The price is steep, no question, but decent primes in FF are not cheaper.