What is the best m43 for focus tracking?

Started Mar 31, 2013 | Questions thread
Anders W Forum Pro • Posts: 21,468
Re: what is the best m43 for focus tracking?

JamieTux wrote:

Hi Anders, I was just talking in relation to tracking AF - and I was thinking that if you take 2 readings and the second is further than the first then you know very quickly the direction of motion.  I wasn't talking about it being THE trump card for everything

We are probably thinking along roughly the same lines. But I find it interesting to consider the details of when and to what extent the ability of PDAF to tell whether the subject is in front of or behind focus and the direction and speed of the movement translates into a clear advantage. Consider to begin with the following examples.

Example 1: Suppose that for a single shot (not a burst), we press the shutter fully, without having half-pressed to prefocus, while aiming at a new moving target. In this case, CDAF is likely to do just as well as PDAF, perhaps better. The circumstances are essentially the same as when focusing on a static target.

Example 2: Suppose we instead try to prefocus on a moving target and then expect the camera to keep that target in focus while we wait for the proper moment to fire. In this case, a known difference between CDAF and PDAF is that CDAF has to adjust focus a little all the time in order to even know whether there is any motion that brings the subject out of focus whereas PDAF doesn't have to do that. On the other hand, PDAF lenses have difficulties moving in very small steps with great precision so it might be more difficult for PDAF to fine-tune focus as the subject moves. Furthermore, the inability of CDAF to determine by means of a single AF reading whether the subject is in focus, behind focus, or in front of focus can be compensated for by "learning from experience". If the subject is regularly moving in one direction, an intelligent CDAF system would quickly discover that fact by trial and error and then try the expected focus direction before the unexpected in its attempt to keep the subject in focus, thus doing better than it otherwise would. So it doesn't seem to me that PDAF has a major advantage in this case either.

There are then, of course, the more complicated scenarios of burst-mode shooting, but I thought we might take the simple ones first.

In the above examples, I am just thinking aloud, and I might have missed something important. So feel free to try to correct me if you think I have missed something important.

I think that the biggest factor for trakcing is probably the amount of data that needs to be processed - and not having separate processors for that job as far as I am aware in CDAF sensors - about to reply to Celngman with more thoughts.

Yes. Data processing capabilities are of considerable importance here. But with those capabilities continuing to rise more or less in agreement with Moore's law, there is hope on the horizon.

Haven't had a chance to test the GH3 yet by the way

But you have it already or what?

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