Big vs Small focus square

[Hermelin]

What's the benefit of using a big focus square vs small focus square and vice versa?

[Lumens]

I was using my XT-1 with the 100-400 this weekend with a high shutter speed for a very active event.  I found I was having problems with focus hunting.  I had the focus square as small as it could go - so I enlarged it and no more focus hunting.  In fact, I was able to focus extremely quickly which allowed me some pretty good shots.  I like it small for detailed work, but for quick focus it is a good idea to enlarge it.

[Aswald]

If you have a simple / not so busy background, the larger the square the more you rely on the af system of the camera to grab focus. This is especially so when your subject is smaller than the square.

 

If you have a very busy background / foreground, the smaller square will enable the camera to focus on the subject and not be confused by its surrounding.

 

In bird photography, if the whole bird is within the square in an empty sky, it'll lock focus nicely on the bird. But the same can't be said for a flock of sheep. It may lock on to neighboring sheep.

[erwiurewurwehu]

My theory is that smaller is generally better and more precise but you need contrast within the focusing area. So something you have to go bigger so the camera can find something to focus on.

[Tom H.]

Small square only for posed portraits with very shallow dof. For everything else I tend to keep it at setting 3 or 4.

[frankinfuji]

Small square only for posed portraits with very shallow dof. For everything else I tend to keep it at setting 3 or 4.

 

Same for me.  For narrow DOF portraits I use the smallest square and place it over the nearest eye.  But for more general work - such a small square may cause slow focus - as there may not be much contrast in the small square (I think), so I use a bigger square or zone focusing.

 

I have three of the rear buttons (the top and the two side buttons around the circle) all set to focus on my X-E2 (firmware 4), so it's easy to move the focus point with one push, then use the wheel to change the size if needed.

[Scott Grant]

Big focus square = speed of focus but less precision
Small focus square = precision but slower focusing