Idiot question alert - 52 focus points

Started Jan 2, 2014 | Questions thread
Grevture Veteran Member • Posts: 4,188
Pretty simple actually ...

paul2009 wrote:

hmm. So is it that with numerous AF points the camera takes an average? What is the advantage of having so many AF points? Surely, in the end, the camera only focuses on one part of the field?

Before even looking into details of different focus modes, just think of it in very simple terms:

- If you want to measure something to make a decision (where to focus), do you want to base that decision on just a little information or on more information?

More focus points makes it possible to get more detailed focus measurements. It's that simple.

Now to step up a bit:

Think about measuring exposure, do you want it in just one spot in the middle, or do you want to measure many spots and make various calculations (averaging etc)?

Well, in most cases you want to be able to do both. That is why we have options like matrix exposure where the camera makes lots of measurements and analyze the result in various ways, and also simple spot metering where you measure at one point only.

Focusing works pretty much the same. Sometimes you just want to measure in one spot and completely ignore what is going on around that spot. Sometimes you want to measure over a smaller area, and ignore things outside that area. And sometimes you want to measure over a larger area and figure things out from all that information.

And to enable these different ways of focusing, you want as many focus points as possible. Sometimes you use just one, sometimes you use several or even all of them. And, sometimes when even when measuring with just one focus point, you want to be able to move it outside the (default) center spot. More focus points just means more options available for measuring focus. Pretty simple.

Personally, I switch around a lot between single spot, and area modes (9, 21, 51), and I often move around the main focus point. Having 51 works well, but I would not mind even more of them.

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