If I believed that a camera with AF best met my needs/wants/desires, I'd have lots of choices from several manufacturers. Preferring to use a digial SLR optimized for manual focus, my choice is limited to a single discontinued model. I have no problem with other's preferences, there's a wealth of AF cameras available.
As I mentioned before in this thread, it is the reason why
you prefer something, which is more interesting than simply the fact that you prefer it.
So far, you've mentioned just one lens that you use, and even boasted about its sharpness in the corners, the Leica 280mm f/4 APO-Telyt-R. As far as I'm aware, this lens could not autofocus even if you wanted it to
I understand perfectly, if you are in the habit of buying lenses not designed for the camera, because they are the sharpest lenses available, and because maximum sharpness is a priority for you, then autofocus is either not an option, or, if it is an option, it might not pass muster in its current state of development, especially if you frequently use telephoto lenses at wide apertures and/or insist on achieving the maximum sharpness that your lenses are capable of.
However, this is not my situation. Having taken photos with film cameras for a good many years, at least sporadically, as an amateur, I recall that some of the major improvements in camera technology which tended to renew my interest in photography, were (1) The built-in lightmeter, which inspired me to buy my first SLR, the Pentax Spotmatic.(2) Autofusing, as in the Minolta 7000 which I bought in the mid 1980's, and (3) Image Stabilisation, as in the Canon 100-400 IS zoom, which I bought with my first DSLR.
I value such features and would not trade them in for some potential, slight increase in resolution. That would be like 'throwing out the baby with the bathwater'.
My secondary mission is to tell y'all you don't have to be so damned dependant on the technology. The technology is fine in the right context but AF'ers don't need to be so afraid of trusting their own eyes and hands.
Being afraid of trusting my own hands and eyes is not the reason why I
use autofocus. It's all about 'getting the shot', for me. There's a lot to be said for 'F8 and be there'.
There is also an issue that too many technical concerns and adjustments, required to be made during the framing of a composition, can get in the way of one's observation of the overall scene. In my experience, during manual focusing, one has to move between focus and out-of-focus on both sides of the target before one can be certain one has the sharpest setting. This not only takes more time than autofocusing, but detracts from one's awarenesss and appreciation of the composition as a whole. It's no wonder you sometimes end up with a bird in the extreme corner of the frame.
However, I freely confess that I do not specialize in bird shots, particularly birds in flight, or football matches or other sporting events where quick and erractic movement takes place. It might well be the case, if I were to test my equipment in such situations, I would find autofocus tracking inadequate.
Nevertheless, it would be very odd, after declaring the possession of a 100-400 zoom, if I had no shots of birds. Of course, I do have a number of shots of birds. Perhaps not in the thousands, but certainly in the hundreds. Most of them were probably taken with my first DSLR, the Canon D60, with its miserable 6mp.
Here's one such shot, attached, taken in February 2006. It's clear from the expression of the two Frogmouths on the right, that they are very skeptical of your claims for the benefits of manual focusing.
However, the two on the left clearly don't give a stuff.