THIS TEST WAS DONE IN AUGUST, 2017 WITH THE LATEST FIRMWARE UPDATE FOR BOTH THE A9 AND LA-EA3 ADAPTER: I shot a minor league baseball game with the Sony A9 with the Sony LA-EA3 adapter (with firmware update to allow AF-C) and the Sony SAL300mm f/2.8G SSMII lens. The results were good and the connection was never broken the entire game. I found the combination more than workable and got very nice results, though nothing like what the images would have been like with an FE mount lens and no adapter. The Sony 300mm f/2.8G lens is superb and offers very fast AF, excellent sharpness and 10 FPS is possible on the A9 with that combo.
Prior to the firmware update for the LA-EA3, it was not possible to achieve AF-C (continuous AF while shooting at the high fps rates for stills). With the latest update for LA-EA3 AND for the A9, it is now possible to shoot at 10fps WITH tracking AF with A-mount lenses.
