Originally posted by BruceBanner Yes, but when you look at AF lenses, they are all normally below F6.3-F6.7 for a reason.
I began actually exploring this in 1990 when I bought the 1.7x AF converter to ass limited AF capability to my legacy lenses on my PZ1.
At the time the converter was rated for use on F2.8 and faster. But it works very well on F4 lenses, and didn’t work with f5.6 lenses at all.
Since then people have reported limited success on lenses on F4.5 and intermittent work on F5.6 lenses. If you consider the 1.7x converter adds about 1.5 stops f4.5 plus TC is F8 and F5.6 plus the TC is About F9.5-10
There are lots of discussions about the minimum aperture needed to get AF lock, or with manual lenses Focus confirmation. They all center about F8. As a max aperture limit