OK, just got back from a trip to Namibia and South Africa. Lots of animal pics. But the new-to-me 100-400 was giving me fits. It would refuse to auto-focus at the oddest times. Turn it on, focus, snap-snap-snap. Pause a moment to just gawk at critters, then try to shoot again, nothing, Nada. Red box. I had to turn it off, wait for it to re-set (hear the "clunk") and then turn it on again. Or switch to video, wait for it to start focusing, and then click back to stills.
Internet connectivity was slow (like, close to dial-up speed) so it took me a while to get the info.
A setting needed changing.
"Lens drive when AF impossible" was OFF. When I changed that to "On" the camera and lens ripped along with abandon, focusing even when I thought it not possible. (Like a Leopard, and later, a pair of lions, at night)
Is "Off" the factory setting and if so, why do they do that?
I believe the default setting on that camera is 'on'. It is on my R100. Did you buy the camera new or used? If you bought it used, the previous owner may have turned if off. Just a suggestion
Jim
