Is Safox X really more accurate with fast glass?

Started Jan 21, 2013 | Discussions thread
Winder Senior Member • Posts: 1,460
Re: Can someone explain what the difference is between a 2.8 and a 5.6 AF sensor?

KL Matt wrote:

I never understood this. Niether how it impacts performance nor what it means from a technical perspective.

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... interested in .... photographs? Heh? Know what a mean? Photographs? (He asked him knowingly). Nudge nudge, snap snap, grin grin, wink wink, say no more, say no more, know what a' mean? Know what a' mean?

I will attempt and try not to screw it up too bad.  The farther apart you can set the AF sensors the more accurate your AF system, but you need a wider aperture to move these point farther apart.  Remember PDAF is a "phase" AF system so two images have to be in "phase" to focus.  The farther apart these sensors the more accurate the AF.  A lens that only opens up to F/4 would block the F/2.8 sensors and the camera would have to use the F/5.6 sensors.

The improvement to AF will only be seen with lenses that are F/2.8 or faster.  Below is a drawing from Canon.

See how much farther apart the F/2.8 sensors are compared to the F/5.6.

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Contax 645, Canon 5D (sold), Olympus E-3 (sold), Playing with a K-7 and K-5

 Winder's gear list:Winder's gear list
Pentax K-3 Sony Alpha 7 II Pentax K-1 Sigma 50mm F1.4 EX DG HSM Pentax smc FA 31mm F1.8 AL Limited +4 more
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