When shooting at or near the full telephoto with this and the kit 55-300 the autofocus loses the subject (usually flying birds against a featureless sky) after one or two rapid exposures and when it does, the attempted auto reaquisition takes the focus from near infinity down into the near macro range where it stalls and requires a manual refocus. Zooming out and pointing at some closer, high definition subject will also move the focus out towards infinity. It seems to do this no matter the focus settings - single point, AF-A,C, Dynamic, whatever. Because of the rather unique nature of each target aquisition and flight path, it is not something I can systematically test. Any suggestions from more experienced photographers? Tom Forker
The simple explanation would be that you are not keeping the birds under the focus point during the frame burst. AF-C and dynamic mode would be my starting point. However, you may have already covered that.
---------+---------+---------+---------+ Joseph K Seattle, WA, USA
It is almost certain that the focus point moves off of the bird, but I am most perplexed with the camera process of searching down to minimum focus distance and "freezing" there even if I lift my finger from the shutter button and attempt to refocus. I suppose that many, if not every time, there is no longer a target in the field of view but it would seem that a "logical" process of autofocus would search back towards infinity rather than stalling at minimum focus.
Once you've lost focus on a bird in flight and the lens starts hunting, you're probably not going to get it back by trying to follow the bird. Try pointing the camera at a distant point on the ground and focusing, so the camera's focus is set for a distant target. Then aim at the bird and when the bird is under your focus point, you should be able to get it in focus and get your shot. The 55-300 does not have a focus limiter switch (which would help, if the lens had it). There is a learning curve for this type of shooting, so I think you will find that with more experience you will be better able to get those shots.
Thanks to all for taking the time to respond. My key question, and I should perhaps have stated it more clearly, was why the focus system pushes the lens out to macro territory and then leaves it there. In practice, I usually do what was suggested and point down to distant ground or trees where the camera can capture some high contrast subject material. Are the higher priced cameras any more capable of "intelligent" search? Tom Forker PS I will post photos of some more successful adventures when I can sort out the gallery process.
Tom. I tried to duplicate what you get with my D5100. I don't have either of your lenses so the closest I could get with a f5.6 zoom at the long end was with my AFS VR 18-200mm lens. When I lose focus with that lens it stops searching at infinity and not the close-up range you're seeing. I use AF-S and center focus point in aperture priority. Maybe somebody that has either of your lenses can give it a try.
To answer your second question about the performance of higher prices cameras I can only say maybe. I don't know if they are more "intelligent" but they do have more improved auto focus systems in the number of cross type sensors and maybe better response at the f5.6 range.