Will the A7711 be mirorless

Started Apr 2, 2014 | Discussions thread
JamieTux Veteran Member • Posts: 4,079
Re: Will the A7711 be mirorless

123Mike wrote:

EinsteinsGhost wrote:

EinsteinsGhost wrote:

I think the translucent will be gone with the A77II. Just my thought. Looks like the A6000 is performing really well and with a big buffer of about 50 shots at 11fps. What more do you want? And better noise performance.

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www.alex-digitalpics.be by Sony

It won't be that simple. If the focal plane AF system does not work well with older lenses, SLT is here to stay, even part time (as in depending on the lens).

"Also note that these focusing problems are never a lens problem but always a camera problem! Auto-focus is a feedback loop, and the camera will move the lens to what it considers the best focus. If you had a lens with a slightly misadjusted focusing barrel, the camera would simply move the lens further or less far to achieve an in-focus image"

Ok, so, sensor sees image. Image out of focus. Camera moves focus. Camera sees focused picture. Done. Not?

Its not that simple. The lens has to do so very very quickly or we end up with slow AF (and in case of CDAF, jerky movement).

PDAF lenses are driven straight to the point in focus (or almost as precise as it can be). CDAF lenses use evaluation of contrast often going past and returning back and so on as a feedback loop. So, CDAF requires frequent change in direction whereas PDAF goes in one direction.

The evaluation phase would be the trouble maker for PDAF lens (put an A-mount lens via LAEA1/3 on E-mount camera and you will experience it). That is because the AF motor is not designed for it. This also happens with Live View in DSLRs with lenses designed for PDAF only.

But *if* the sensors offer full time PDAF, the camera can know how far off the focus is. Or do you think that sensor based PDAF isn't as good as dedicated PDAF?

I think you're missing the point a bit Mike.
EG is talking about the mechanics of the system - not a particular use case scenario.
The big advantage of PDAF is that you can see how much something is out of focus - so you can tell the lens where to go - and then reassess again.
Contrast cannot do this - in fact it can't ever tell if something is in focus (put a CDAF only camera into AF-C and focus on something still - you'll see the image get out of focus at times as the camera moves focus to check that contrast is as high as it can be).

So at the moment the point is not about accuracy - it's about the mechanics of how it works and the competing requirements in lens design.
I would look at the Olympus OMD EM1 to get an idea of how compromises can work though

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