Shooting the 100-400mm GM and 70-350mm G on the a6500 this afternoon showed the APS-C lens to be noticeably sharper than the “pro” lens. Yeah, confirmed I got a lousy copy.
On the bright side, some reading turned up a suggestion for getting faster AF with the crop sensor setup: leaving “Setting effect” switched off. That’s an option for the exposure preview that many cameras do by default nowadays. Easiest workaround for me was to leave EV at 0, same basic result; and it worked. Not blazing fast, but fast enough to get a decent keeper rate with small, flitty birds. Its biggest limitation now is the a6500’s noise.
Now . . . what to do with the GM lens? There’s no reason whatsoever to hang on to it, with it being outperformed by a much lighter, far more compact lens. But the only alternative that works with the extender (other than the unattainable primes) is the 200-600mm. And the RF 800mm is better, lighter, smaller, and has more reach for that application.
Sigma 150-600mm? No, another oversized one. It occurred to me that I could grab a Canon EF 100-400mm IS II and adapt it to Sony with the MC-11, but with a teleconverter it’s just as heavy as the other two, but with less reach. In the right size range, Sigma 100-400mm, but with firmware issues that didn’t get solved along with the L-mount version, and teleconverter has not been available anywhere for eons.
A moderately fast manual focus prime might work nicely, and my accessory closet has adapters for attaching damn near anything to Sony, which also works extremely well with adapted lenses. But what? Anything reasonable would likely be heavy and no better than the zooms I already have.
Gotta think of something, though; the a7 IV is too good to sit idle in the dry cabinet, and deserves some good glass.