Quote Originally Posted by bitsnpieces View Post
.... (don't know if the a77/99 has hybrid or now, but definitely my a65 doesn't )
AF ability and features is an important feature distinction set that manufacturers use to separate lower end models from higher end models.

And just to be clear on this face detection issue: The problem of face detect and the af points happens irrespective if you are using the viewfinder, or if you are using the rear LCD screen to shoot?

I find it strange if the issue happens in rear lcd shooting mode.
When using the vf, it makes sense that face detect(if it works) would be tied to the AF point only if face detect via phase detect were possible.
But it may seem that it isn't.

The way PDAF works, is that the PD sensor basically splits the in coming light beam of the object into two different phases(think of it in a similar way to those red/blue 3D glasses.
If you know how a rangefinder focusing system works, then you get the idea of what a PDAF system is doing in a basic sense.
When the two phases are in sync, ie focused .. the PDAF systems recognises it as in focus.

A CDAF system looks for contrast between adjacent pixels. At it's most basic image in black and white line(Collingwood jumper) pattern. When in focus the difference between the black and white lines is sharp and obvious. CDAF sees this, but it takes time to see it clearly. The CDAF system has to focus defocus in small steps to see where the best sharply rendered difference lies.

Where PDAF deliberately splits the image and then uses that split to recombine it again into a focused image, CD sort of has to construct the image it needs to see from the start.
There's a ton more programming smartiness in CDAF, and hence why it also recognised faces .. and so many types of faces.

I don't know for sure, but I don't think PDAF can have the sort of programming to recognise specific objects(such as faces, or features).
it's prgrammability seems to be limited to recognising only colour, or patterns of colour(subject tracking).
It doesn't know the subject being tracked. It just recognises the differences in colour between it and it's surrounding area.


I'm just surprised that in rear LCD shooting mode, the a65 wouldn't have full time CDAF and hence full time access to face detect.

On the D800, when in liveview mode(rear LCD shooting), the PDAF points aren't active. The CDAF system is totally independent of the PDAF system. There are no AF points as such(except that you can snap to the centre with one action if need be) .. the entire sensor area is an AF point.
But CDAF is slow as hell and you wouldn't use it for every day focusing.
Once it's focused and tracking faces tho, and if the lens is fast enough to hold focus, it can be useful if needed.

In fact this is the first time I've actually turned face detect on and tried to see it in action.