Autofocus Blues

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spiritcat Forum Member • Posts: 50
Autofocus Blues

Hi. I posted this in one of the entrance hall forums, but I forgot that this sub-forum existed and since it is specific to D850, perhaps this is the better place for it. I didn't intentionally mean t double post, so if that's a problem, and there's an easy way to remove from the other, let me know.

Not quite a complete beginner, but I don't consider myself an expert. Took wildlife pics with Canon T2i for 2 years, and then just recently upgraded significantly to Nikon D850. I have been using this with the Sigma 150-600, and was looking forward to the lightning fast autofocus I had heard so much about, that would enable me to track birds in flight.

What I seek to know is whether the behavior I am about to describe is normal for the d850, or whether I have a problem. I have been having a number of difficulties with focus...difficulties that I did not really have with the T2i. With the D850 I still find the autofocus quite "sticky" when tracking a bird in flight. For instance, sometimes, with AF-continuous engaged, I have the center point (or 9 points or more if I am using dynamic area) right on the bird for long seconds before anything happens. So long in fact that the shot is lost before the AF acquires and the bird is in focus. Sometimes it has more or less circled round past me by then! Again, this doesn't happen all the time, but seems to happen, say, one in every four times. I understand that autofocus is not magic, and has its limitations according to complexity of background etc, but again, what I am discussing here is sometimes a bird against clear sky. And while sometimes it does seem to acquire flawlessly, sometimes I have af-c on, but nothing is happening, and I seem to have to "jog" it by taking my finger off the back-button focus and pressing it in again.

Is what I am discussing normal behavior for the D850 or do I have a problem?

I'm also quite prepared to accept that it may be technique, especially as I seem to be having other focus issues. I recently got back from photographing a whole bunch of birds on an island, and many of these were not quite in focus, even the shots of static birds.

Am I also correct in saying that one should not attempt to use AF at all if shooting at f9 or above? I mean, the AF can sometimes "work" in those situations, but is it common practice, thinking of wildlife in particular, to always focus manually at f9 or smaller in aperture?

Canon EOS 550D (EOS Rebel T2i / EOS Kiss X4) Nikon D850
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