Where do I even begin? *big post*

[arthurking83]

.... (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.

[bitsnpieces]

That's a very interesting point posted up there, that when using liveview, it should go into CDAF mode - based on Sony's little diagram, it would seem that should be the way it works (given that it has hybrid AF) - I'm going to double check my settings to make sure I haven't set something that is blocking this.

Or I could check Google to see if a65 has hybrid AF or not :P Who knows... Maybe one feature Sony took out from the a65 to become the little brother to the a77 is hybrid AF...



Okay, I'm calling it, the a65 has no CDAF, even Object tracking didn't focus unless it was on an AF Point.
Basically, everything relies on the AF Points - if what you want to focus on, face, object tracking, etc, the initial focus won't happen unless it's on an AF Point, and the camera will just focus in the centre or whatever it likes.

Face Detection priority works the same way. You put priority on a face, but the AF Points line up to a different face, it'll face the other face - so priority only works if there's an AF Point on it also, then out of the two faces with AF Points, it'll pick the priority face.

Using AF Centre or AF Spot (or whatever it's called when you pick an AF point) will override Face Detection. It will also focus in the centre or the AF Point chosen, never on faces, pretty much.

Also, I could not get Face Detect to focus on multiple faces at the same time, it always focused on one only. When I put object tracking on the far right, then went back to get both faces on AF Points and the object tracking out of one, then the camera focused both faces sometimes, most of the time still only focused on one face. And now because the object tracking is left dangling far right, it easily loses focus of what it's tracking and turns off.

Well, I think this concludes my theory and also verifies that the a65 isn't using CDAF, and if it does have it, I have absolutely no clue how to access it - menus all seem fine.

[arthurking83]

There may be a subtle difference between object tracking and CDAF on the little Sony.

I find it weird that Sony wouldn't have CDAF on a camera that is heavily biased towards video.
PDAF is either rare or non existent in video modes, and all cameras I know of use CDAF.

So ...

maybe you need to be in a normal non tracking type AF mode(well maybe face detect or something) AND you may need to use one of the automated scene modes to get the camera to use CDAF or something like that.

First off set it to video mode to make sure that it won't use the PDAF sensor points.
Then once you can confirm that video mode does use only CDAF, then you know that you have a CDAF only mode.
Once you know this, try setting the camera to a scene mode(Portrait would be the most obvious choice) and see if you can get CDAF only whilst trying to track and focus using liveview mode(not the evf mode).

Just had a read of DPR's review of the a65, and it looks like the video mode does rely on the PDAF system, as does tracking.(gives info about face detect mode tho).
DPR says that for video mode and AF, you need to set the camera to Program AE mode. If you try M, A or S modes, you don't get AF in video mode as the limitation is that the aperture needs to be set to f/5.6 or larger. This is always a limitation of PDAF sensors at the cheap end of the market, higher end PDAF cameras work down to f/8 nowadays.

So it seems that the a65's focus system is limited heavily in many ways.
DPR also goes on to summarize that while the focus is generally good for most situations, fast paced action is a weak point for the af system.

[bitsnpieces]

My next test was to try one of the modes, and forgot to do it today when I had the chance *dough*

But yes, that is something to test to see if CDAF is condition or not.

I'll try and video too - I believe I should have time later today

[kevin301]

The interesting thing about the Sony SLT range is that because of the fixed translucent mirror, there is always light falling onto the AF sensors during LiveView. Thus it presents a rather unique scenario of being able to utilize the AF sensors for PDAF, and the image sensor for CDAF. With typical DSLRs, you either get 1 or the other

As Arthur mentioned, the AF sensors for PDAF work on beam splitting and analysis to determine the focus error. This system would not be able to recognize faces.

Therefore I reiterate my stance that because of the different nature of PDAF and CDAF, it doesn't make sense for a ("gimmicky") feature like face detection to be able to work with both

Perhaps the camera is simply going "Hey, here's a face I detected. Please align it with one of the AF points so I can use PDAF for more accurate focusing"

[bitsnpieces]

I believe you're right Kevin - there's just no way to get anything to be focused unless they're on one of the AF Points.
I've tried the portrait modes and movie mode - gotta be in the square.

So it's unfortunate - though using PDAF which works fast, there are still many limits such as a small area of focus, and if anything ever happens outside of it, or for convenience, it doesn't cut it.

Well, I guess you just work with what you have, but the other disappointing factor is that it only focuses 1 face at a time, rather than multiple, even if there are multiple faces lined up onto an AF point... :S

Well, case closed.

[arthurking83]

so when the face detect system is on, and it sees the faces off the PDAF sensor area, does it recognise the faces?

The way I've seen face detect working is that it finds a face(or faces) and then follows them(phone, DSLR and P&S... they all do this)
If it recognises the faces, the colour of the squares determine if it's being used for focus.

So if you have multiple faces detected, and some of the squares are yellow or red, and others are green, then it's obvious that the green ones are the ones being used for focus.

CDAF is much slower to operate than PDAF, so it may not be immediately obvious that AF is working. The colour of the focus highlight is a better indicator.
And don't assume that becasue the image is blurry it hasn't been focused correctly either!
So many factors come into play for a sharp image, it's hard for a newbie to discern misfocus from camera movement, from subject movement, from ... etc.


I think Kevin hit the issue on the head here:

...... Thus it presents a rather unique scenario of being able to utilize the AF sensors for PDAF, and the image sensor for CDAF. With typical DSLRs, you either get 1 or the other

.....

Perhaps the camera is simply going "Hey, here's a face I detected. Please align it with one of the AF points so I can use PDAF for more accurate focusing"

I reckon what could(or at least should) be happening is that while the subject is off the AF grid(ie. on the image sensor and hence CDAF) .. it'll be followed and focused on using CDAF(when in face detect mode).
BUT ... as soon as the face lines up with an area in the AF grid, the PDAF sensor takes over, so it may appear that the face detect isn't working properly.

So are you confirming that if a face is nowhere near the PDAF grid, that if face detect is used, the camera simply will not focus on that face. Nor will it follow the face(as an object).
Remember too, CDAF is not always obvious in it's operation. I'd determine the colour of the focus area as an indicator of whether it's focusing, focused or not.

On Nikon cameras(well the D800 that I know of), a detected face in a green square is in focus, and a face in a yellow square is not(in focus).
it's actually a bit annoying(if you choose to use face detect that is), in Nikon choosing a yellow colour for the af square not in focus
In normal CDAF is, a focus square not in focus is red.
So the inconsistency can cause confusion. The difference in the yellow and green is pretty obvious, but for folks that have even a partial colour blindness, the difference between a green and a yellow may not be distinct enough.

[kevin301]

I believe you're right Kevin - there's just no way to get anything to be focused unless they're on one of the AF Points.
I've tried the portrait modes and movie mode - gotta be in the square.

So it's unfortunate - though using PDAF which works fast, there are still many limits such as a small area of focus, and if anything ever happens outside of it, or for convenience, it doesn't cut it.

Well, I guess you just work with what you have, but the other disappointing factor is that it only focuses 1 face at a time, rather than multiple, even if there are multiple faces lined up onto an AF point... :S

Well, case closed.

I wouldn't be too concerned about the camera not focusing on multiple faces at 1 time, i.e not having multiple boxes lined up on the faces. The nature of focusing is that it is by distance (from the camera). Therefore if all your subjects are aligned more or less along the plane of focus, getting 1 of the subjects to be in focus should cause the rest to be in focus as well.
Of course I say this very casually, ignoring some factors such as use of fast lens (e.g. f/1.4) or focusing on a near subject, which results in a particularly thin depth of field.

[bitsnpieces]

True that.

Though we talked a lot about Face Detection in the post, at the end of the day, it was trying to understand the autofocusing function of the a65 - so I think I understand how it works a lot better now, the capabilities, expectations, and how I should use it.

Thank you everyone for your inputs.