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some days ago I daring duck had approached while I was taking photos of her and her friends in a pond. I was testing my new 70-200 2.8 VRII and I was a bit worried about the autofocus while working with autofocus and VR (camera was handheld).

The was duck at my feet and given that I was standing and I'm 1.76m tall, I think more or less the distance between the first lens and the duck was 1.20m.
I managed to take some perfectly focused picture of the head of the animal while I was using 120mm (again, at the moment I'm not totally sure since I haven't the foto with me).

I was using the "FULL" range of autofocus, but having read in the instruction that it would go much faster if I set the switch to "< 5m" I tried it. Results? The Autofocus couldn't "find" the head of the duck anymore. I switched back, it worked again. Again to "< 5m" and it didn't.

What the hell was wrong? Do I have a flawed objective?

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That lens has a switch that limits focus from 5m to infinity. The other setting (full) lets you focus from 1.4 m to infinity. There is no setting to focus between 1.4m and 5m only. You cannot focus on anything closer than 1.4 meter with that lens.

Manual here: http://cdn-10.nikon-cdn.com/pdf/manuals/lenses/AF/AFS70-200_2.8GEDVRII.pdf

I use the 5m - infinity setting when I shoot sports with that lens. When the lens can't find focus it might try to find a point very close by. The time it takes to go all the way back again to a point further away might cost me a shot. Limiting it to 5m is ok since I know the action is always further away than that.

  • Aw! I really misread that :/ – Noldor130884 Dec 19 '14 at 13:02
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    That's handy to know as on the 80-200 f/2.8D limit switch locks focus to either side of the limit depending on where the focus was before you flicked the switch. I'd have expected newer lenses to be the same... – James Snell Dec 19 '14 at 13:46
  • @JamesSnell: The limit switch on AF-S lenses is electronic, so in theory the limit is in the firmware. On AF, it's mechanical and adds a physical obstacle to the focus ring. (It's also interesting to note that the Mk I version of the 70-200 limits at 2.5m, which makes it much more useful for portraits.) – Blrfl Dec 19 '14 at 15:53
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Most good telephoto zoom lenses have that same feature. As Rene points out, the switch is to make the minimum focus distance further away rather than closer. The reason you do this is to reduce the range of values that the camera needs to consider focusing on, thus making it quicker and easier for it to find focus. It does, however, mean that the lens will never adjust to the focus position for something closer than that distance using AF.

You can still manually focus on something closer, but the AF will no longer bother checking or trying to focus on something within that close of a range. In general, you want to use the setting whenever you know for sure your subject will be further away and only turn it off when your subject may be within that range.

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