With the world’s fastest autofocus system (A6000)

Started Feb 12, 2014 | Discussions thread
EinsteinsGhost Forum Pro • Posts: 11,977
Re: re: few questions on practical aspects of the a6k

erringtont wrote:

EinsteinsGhost wrote:

erringtont wrote:

My original question, in a reply to JPR2 post, was in regards to the a6k. If the new faster AF system in that camera is available at all, or higher value apertures, then that is an improvement and would be an item I would take into consideration if I were to upgrade.

It doesn't happen with DSLRs, it won't happen with mirror-less. Smaller apertures and/or lower light reduces AF performance in every camera.

A realistic expectation will be to expect a6K to perform like a DSLR/DSLT would with a lens that is capable of focusing fast.

I agree. The top current DSLR autofocus systems will work with lenses who's maximum aperture is f8.0 or wider (on my D-300 it's f5.6). But I believe that is a different issue.

Its not. The issue is reduced light, making AF system less effective. In fact, at apertures smaller than f/5.6, even DSLRs like D800 all of their outer AF points.

A key issue with focal plane AF currently is that pixels are smaller, but if developments are made to work more of them as one, they could potentially have greater low light capabilities, also because focal plane AF receives 100% of the light (mirror based AF systems don't, as part of the light goes towards metering).

If the lens on my DSLR has a maximum aperture of say f4 or maybe a range of say f3.5 - 5.6 the autofocus functions at any aperture I may have set for the exposure as it is focusing wide open.

Sony is stating that the NEX 6's PDAF is not available at aperture values greater than f6.3 and only contrast detect AF is available in those circumstances. Likewise on the A7, PDAF is not available at aperture values above f8 (f9 and higher is how it is stated). So regardless of the maximum aperture of the lens in use, setting an aperture for the exposure that is above these limits defeats PDAF. That is my understanding.

My question is not so much about focus speed but when is PDAF actually working. Is the a6k with it's newer PDAF still active at exposure aperture values above f6.3. My guess is yes since the A7 has a higher spec, but Sony has not published the documentation as yet, so we'll have to wait and see.

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