Will the A7711 be mirorless

Started Apr 2, 2014 | Discussions thread
JamieTux Veteran Member • Posts: 4,072
Re: Will the A7711 be mirorless

123Mike wrote:

JamieTux wrote:

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.

-- hide signature --

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

I know all this. I know that the mirror based systems, the camera can know how much it is out of focus, and can direct the lens with one focusing motion to the desired spot. Or in a few moves, but each step the camera can make a good guess how much to move. And that with CDAF it is a homing-in process requiring the lens being able to focus back and forth without play. With CDAF it's a let's-move-until-we-see-something-we-want type of deal.

It's PDAF that works that way - it's not dependent on a mirror.

My point was that if sensor based PDAF can not see how much something is out of focus very well, then A-mount lenses will likely not perform so well on a mirrorless system. Or that's what I thought EG's point was, and I see that point and I'm making that point also. However, the question is, *if* on-sensor PDAF is as good as mirror based, *then* A-mount on mirror *should* be able to perform just as well. The A6000, even though it has a ton of PDAF points, it also has a ton of CDAF points (why CDAF can't just be across the whole sensor is another matter). But... in tests so far, we're not seeing any hunting whatsoever. I have the feeling that the new on-sensor PDAF does it better than mirror based, and that A-mount lenses can work perfectly well and very fast on mirrorless.

Which could work out well - I *think* that EG is basically saying we will have to wait and see.  Unless you know something that I don't there's no way of seeing how the whole system works together with any a-mount lenses (and certainly not all of them).

 JamieTux's gear list:JamieTux's gear list
Nikon 1 J5 Fujifilm X-E3 Nikon 1 Nikkor 18.5mm f/1.8 Zeiss Touit 50mm F2.8 Nikon 1 Nikkor VR 10-30mm f/3.5-5.6 PD-Zoom +6 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow