Getting really excited about a77 II

Started Mar 3, 2014 | Discussions thread
123Mike Veteran Member • Posts: 4,643
Re: Mirrorless pls

EinsteinsGhost wrote:

Edward Sargent wrote:

If you have old lenses don't wish for a mirrorless A77 II. Current issues with current phase detect would render them to only MF mode.

Hey Sarge, why would this be the case?

I don't think that will be necessarily true but screw drive and CDAF may be a difficult, if not impossible match. Focal plane PDAF itself won't be an issue but mating the lens to CDAF might be.

And if that is the case, optimal solution may be offer a hybrid set up: high transmission mirror for lenses that won't get along with focal plane AF (hybrid) system, mirrorless for those that do.

I'm starting to think that this could actually be at least partially correct.

If there is a tolerance, a play, rather, in the drive mechanism, it might be that the camera can not predict, when the starting of the focus motor is engaged, that when the lens actually starts changing focus. With 100% pdaf it could be that it simply observes when it starts moving, or rather, when it becomes in focus.

With CDAF, it can not really know when something is perfectly in focus, until it has seen where the peak is. It has to go past the peak point to know it has passed a peak. So with the E-mount lenses, they're super tight and have no play. The focus motor is inside, and does not have any play, and uses a precise stepping motor to drive the focus. When during a contrast focus mechanism, when that focus peak is passed, it can *quickly* backtrack.

But, with a body screw drive, there are all these gears and what not. The camera will not know "how much" to backtrack, so to say. I might have zoof back and forth performing a multi-pass, slower, ritual. Like what we see with the LA-EA1/3 adapters.

Now, why that would also be with a SAM or other in-lens motor system, I don't know. Perhaps the same deal. It can not know in advance how much to drive that motor backwards when it crosses that focus peak. Perhaps it *could* with some lenses, but not reliably across all lenses.

Does this sound reasonable?

Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow