With the world’s fastest autofocus system (A6000)

Started Feb 12, 2014 | Discussions thread
jpr2 Forum Pro • Posts: 15,412
re: not necessarily

erringtont wrote:

jpr2 wrote:

erringtont wrote:

I also took a look at the A7 documentation and it appears this has been improved on that model but is still limited:

"When the aperture value is F9.0 or above, Phase Detection AF cannot be used. Only Contrast AF is available."

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.

is your question set out of purely academic interest? What lens it might be to have aperture f/8 wide open??

I'm assuming of course that a6k will allow a modern setting of focusing wide open, and closing the iris to a predefined value only upon shutter release!!


I suppose it is academic in that we don't have all the specs on the new a6k as yet.

But, my question is simply this:

When is PDAF working (active)?

First, let's assume the lens on the camera is PDAF capable.

On the NEX 6 & 5R, according to Sony, PDAF is not available at aperture values above f6.3. On the A7 PDAF is not available at aperture values above f8. This information comes from Sony's documentation for these cameras. Unless I'm wrong, these aperture limits have to do with what aperture is set for exposure not the maximum aperture of the lens.

For example, if I'm shooting the NEX 6 in Aperture Priority mode with the 16-50 kit lens and have selected f8 for the aperture the camera is using only Contrast Detect to acquire focus.

Since the A7 specification pushes this limitation up it represents an improvement over the NEX 6, perhaps the a6k will exhibit similar improvement.

  • all will depend HOW the actual PDAF algorithms are implemented on a6k;
  • to give you an actual example from another system I know very, very well: Eos 7d;
  • it is an APS-C body, with PDAF limit set by its hardware at f/5.6l
  • yet it is perfectly possible to shoot it even at f/16 (if the lens used is not prone to diffraction softening at such small iris opening) using aperture priority AND utilizing PDAF for very good focusing;
  • why? because all AF'ing will be done at the lens set wide open!! and iris will be closed only upon actual exposure taking place (just a bit earlier than the shutter release);
  • with Nex'en it is a bit different - and I'm not familiar with every Nex camera sufficiently to give you exact details: with some it is possible to operate them in the same way as described for the 7d;
  • I certainly can shoot my Nex7 this way with EF lenses mounted through the Conurus/MB smart adapter (SA), or speed boosetr (SB);
  • but the Sony's default is to close the iris as soon as the value is set - supposedly to render the actual DOF in VF, but for me this seems like not good enough a reason to rob the users' of all the AF'ing benefits of the other approach;


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