What is the best m43 for focus tracking?

Started Mar 31, 2013 | Questions thread
clengman
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Re: what is the best m43 for focus tracking?
In reply to JamieTux, Apr 5, 2013

JamieTux wrote:

Don't forget that PDAF does have one very strong trump card...  It knows whether something is in front of or behind the current focus point.

This was the reason for my initial question. I understand that PDAF systems have a definite advantage with regard to C-AF because can calculate at each instant whether the subject is in front of or behind the focus point. That allows the camera to react more quickly to subject motions in the z-axis. Though, apparently the differences in C-AF performance are shrinking.

It doesn't explain to me though why a PDAF system would be better at tracking C-AF where the problem is tracking subject motion in the x and y directions. I still don't understand entirely why a PDAF system would have much of an advantage for that task.

I see a slight advantage in that if the camera sees a blob of light that seems to move as a unit in all three axes, it's likely to be a discrete object. The CDAF system can look at "blob" movement in two axes, but it's more difficult (but not impossible) to "see" the blob move in the z-axis. (A CDAF system could look at the changing size of the blob for instance, or it can record a value for local contrast across the blob along with a value for focus distance and use that information to plot a z-axis trajectory in which the blob has maximum contrast.)

Otherwise I agree - simplify everything so that the computer has less work to do and it will be faster

I guess this is the compelling argument, but certainly, someone at Olympus must know that if they do some sort of binning operation before they attempt the tracking operation that they can produce a faster tracking algorithm. Perhaps they wanted to develop their system to take advantage of a more complex set of information knowing that it would not be as fast or reliable in early iterations and just count on faster processing in the future to eventually bring the speed of the system up to par?

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