Consider the following comment made on one Web site: “The Sony has 759 phase-detection points that cover 93% of the sensor area, while the Fuji [sic] has up to 425 points that cover 99% of the sensor surface.”
Question: Who wins?
Answer: The marketing departments.
First off, the word “points” in that statement is misleading. The things being described are not points, but are "selectable focus sensor areas." Basically positions to which you could move the Single-point focus marker.
But we’re immediately in a quandary: how fast can you move the focus position between 759 selectable areas? In the case quoted above we have one camera with a higher precision to the selectable area you can choose. But the downside of that is that you’ll be scrolling through more intermediary positions to get to one far from where the camera was set. And given the same size image sensor, doesn’t 759 imply fewer photosites used for focus than 425? What are the implications of that?
Marketing departments love numbers. Canon, for instance, claims 1053 AF areas (note the correct wording) on the R5. At times in the past Canon marketing has talked about many more thousands of focus points (also a correct word in that usage), but that’s not generally how the interface presents focus decisions to the user, so could be misleading in using that number trying to sell the camera.
In short, camera-buying folk seem to love big numbers (61mp!, 1053 AF areas!, 120 fps!, 13-stops DR!). Unfortunately, numbers are mostly being used as selling shortcuts; they don’t tell you much about real capability. Reporting a 13 stop dynamic range, for instance, is always the engineering definition, and I can guarantee you that you won’t like those bottom two stops in that definition (you might not like the top stop, too).
Numbers, of course, are easier to use in marketing than trying to describe a real benefit.
Again, using the comment at the top of the site: which would you rather have, 759/93% or 425/99%? Would you believe neither? That’s right, subject detection came along and changed the whole autofocus marketing claims world. I’d rather have the camera that had the best subject recognition (with appropriate user override). Doh!
