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Topics - Pancho

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Technical Support / Autofocus working conditions
« on: December 06, 2012, 11:01:08 AM »
I have a candid question about autofocus functionality.

Majority of Autofocus are working with a lense at f:5.6.
Some (very) high cost DSLR can work with lenses at f:8.

What is the limiting factor?

Is it the AF system illumination? I'm not sure, because if the AF system can work with a f:5.6 lense at 0EV, it would be able to work with a f:8 lense with 1EV illumination...

Is it a question of Deth Of Field? At f:8 we have more DoF than at f:5.6 and then less precise error measurement inside the AF system.
But if the AF system is able to work with a 18mm f:5.6 at 15m distance, why wouldn't it be able to work with a 400m f:8 at 3m distance?

Thanks for your help.

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