Funny you mention that, the first year I tried hummingbirds (which is to say last year) when I shot the 400mm f/2.8 AF-S VR, I also rented a Nikon 1 V2 (then top of the line) as well as the adapter to F-mount lenses. I was curious what would happen, I tried it with the 400mm f/2.8, as well as my 70-200 f/2.8 and with both of these it was very very slow, and in no way fast enough for the hummingbirds (the way I was shooting them), maybe now with more experience I might be able to more effectively deploy a system like this (and it certainly has its perks with the sensor crop and high-FPS) but it will still suffer in ISO and resolution (though cropping would be less necessary because of the crop factor inherent in the camera)....
That all being said, to your point, the 70-300mm could be interesting since I imagine its AF is way better then with the F mount lenses and the adapter because its built for the system and they are supposed to focus insanely fast....Could be interesting to try next year just for curiosity (and a reviews
) sake.
Personally, I'm also excited for the Olympus MFT 300mm f/4 and 40-150mm f/2.8 lenses since I rented an OM-D EM-1 once and it was pretty impressive, though not relevant for my applications.....but with the 300mm f4 effectively becoming a handhold able (or monopod for stability) 600mm lens on a fast AF body.....will be interesting to try, hopefully that lens will be out by next summer too....lots of fun little caveats to the project....
..also hoping Canon or Nikon release new 800mm lenses just to try out, maybe someone goes insane and makes something faster then 5.6, a man can dream...
Slight Update: also forgot to mention played with the OM-D EM-1 on a 300mm f/2.8 (four-thirds lens) with the adapter at PDN one year (my thoughts are somewhere on my website) and at the time I deemed it too slow, much like the Nikon 1 V2 and the F-mount lenses, so I never bothered trying to rent it, maybe should again.
