Why do some cameras have many autofocus points clustered near the center instead of fewer points spread wider?

Question

My Nikon D3200 has 11 AF points, and I mostly use Single-point AF by selecting one point and placing it on my subject. On newer bodies, there can be many more points, but they often still seem concentrated toward the center rather than reaching all the way to the corners.

Wouldn’t it be more useful to have fewer AF points spread farther across the frame? With my camera, if I want to focus on something near the edge, I often have to focus with another point and recompose. Also, having more points seems like it could make Single-point AF slower to operate.

Am I misunderstanding the benefit of having many AF points? How do extra AF points help if they still don’t cover the extreme corners?

user35348 · Accepted Answer

This is a bit of an apples and oranges comparison, because the D610 is a full frame camera.

isn't it more comfortable to have less focus points wider spread over the whole field instead of like 50 in a small area in the center?

There are two different things here:

number of af points
spread of af points

Now here's the thing: the af points of the D610 are not in a smaller area in the center, the overall image is just bigger. Having more focusing points doesn't mean that they are in a smaller area. In general, the overall area where the focus points are located is the same for the equivalent field of view.

For comparison, I looked up what top of the line crop bodies Nikon offers and found a AF point distribution image of a D7100, which has 51 af points.

I added them all together into one image. The D3200 is dark blue, the D610 is red and the D7100 is green.

enter image description here

As you can see, the D7100 and D3200 have a very similar area of af point distribution. The D610 appears to have a smaller area, but again, it is a full frame camera. I added a scaled image of the D610 and made it more opaque. The scale factor was 1.5, which is roughly the crop factor of Nikon bodies. The scaled D610 area is roughly the same as the one of the D3200 and D7100.

conclusion

The number of AF points can be increased, without increasing the area of the spread. Spreading the points further would require lenses with a more open aperture. That's why the additional AF points are cramped into the same area.
If using a full frame camera, the additional sensor real estate makes the area of the AF points smaller. If switching to a full frame camera, this should be taken under consideration.

Why do some cameras have many autofocus points clustered near the center instead of fewer points spread wider?

2 Answers

conclusion

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