The Sony mount system confuses me - sorry! So you can put an A mount longish lens (300 F2.8/500 F4) on an A7/A9? I thought an adapter would be needed for that? Also, having tried, the Sony 500 F4 I was not impressed. True it has no stabiliser, at least they got that right (!), but I found it slow responding and AF was far from great, images didn't blow my socks off either - then there is the price...........
Unfortunately I don't know of an owner/retailer that would let me manhandle £15k + worth of gear to see if it falls apart. If you do then let me know I would be interested to try and see, but not at my expense.
Let me know if the A mount lenses fit and work when directly connected to an A9/A7 etc - I thought the register distance would require an adapter.
What body were you using the 500 f/4 on?
If it was an e-mount body, which adaptor?
It's not a common lens (given the price), but the reports and images I've seen from experienced Sony A-mount users suggest it does perform well.