On 6/14/2018 6:37 PM, me wrote:
On Thu, 14 Jun 2018 22:41:10 +0200, Alfred Molon
wrote:

In article , -hh
says...
Specifically, when Autofocus capability is disabled when a certain
f/stop value is exceeded.

Why?

If memory serves, the common "upper limit"
value had been f/5.6, with some exceptions at f/8 (such as offered
only on higher end bodies, and/or only at the center focus point).

I have the Olympus 75-300 which is F6.7 at the tele end, but autofocus
works also at the tele end.


Not saying your lens does this but there are those which mis-report
the min aperture (which is used for focusing) to the camera body to
get around this limitation. I have used a Nikon TC-20 and 1st gen
200-400 f/4 VR on D200/300/7100 and 500. D200 while accepting couldn't
hardly focus on the side of a barn. Each focus system has gotten
better, though substantially slowed compared to using a TC-14 which is
my standard go-to with this lens. Min Aperture of f/8 vs f/5.6.


With both my D800, and 500, the only usable autofocus at f8, is center
point focus. i have a lot of problems with tracking birds in flight at
f8, and have resorted to the old fashioned method, hand focus, if I have
to use f8. Have you had a similar issue?


--
PeterN