Am I the only one with AF problems with a zoom lens at f/6.3?

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TheMartyGuy
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Am I the only one with AF problems with a zoom lens at f/6.3?
2 months ago

A few months ago I bought a Sigma 18-250mm lens for my old trusty A200. I just got around trying it out this weekend. At 250mm the lens aperture is f/6.3 full open and the A200 AF is terrible. It hunts over and over sometimes never settling down. When it does settle down, it is sometimes in focus and sometimes slightly out of focus. At focal lengths where the aperture reaches f/5.6 the lens AF is very good.

I know that the A200 requires at least f/5.6 to autofocus (at least according to Sony), so I shouldn't be surprised by its AF at f/6.3.

My question is the following. I am thinking of upgrading to an A57 or A65, Does Sony claim these cameras can AF at f/6.3? I can't find any information in the A57 or A65 manuals about what is the minimum aperture requirement to AF.

Also, if Sony doesn't publish AF requirements for a lens, how does one find such information?

Sony Alpha DSLR-A200 Sony SLT-A57 Sony SLT-A65
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