Understand your Camera – Focus Points, what’s the point?
All DSLR cameras have multiple focus points but do you need them and how do you use them effectively like a commercial photographer?
Yes, indeed you certainly need a focus point or your image will be blurry, but do more focus points mean a sharper image? No, they don’t. If you have your camera set in Auto mode and have all the focus points engaged, the camera will pick one point, which may or may not be the one you wanted, and focus on that. Having many points is beneficial but only when you engage the single point mode which you can then move around in your viewfinder to give you the composition you need.
This makes perfect sense when you understand about your depth of field as that begins on the point you set the focus on. Take these two images below, Image 1 has the focus point set on the furthest wheel and with a shallow depth of field, f 3.5, this means that the while the far wheel is in focus the nearer one is not. In Image 2, the same f-stop has been used but the focus point switched to the nearest wheel meaning that it is in focus and the furthest one isn’t. A simple change but on that that is very effective, of course with a larger depth of field both wheels would be in focus but that wasn’t the image I wanted as it’s for a magazine feature.
Image 1 – Focus on the furthest wheel 
Image 2 – Focus on the nearest wheel
My Nikon d810 has 51 focus points but I only use one at a time, when shooting a person I always focus on an eye and use an f-stop of around f 10 to make sure their entire face is in focus.
When it comes to cars I put the focus point on the badge on the bonnet or somewhere there is a discernable difference in colour or contour. For landscapes or larger images such as a castle, when it’s important that the entire picture be in focus a larger depth of aperture is used, f 18, and the focus point placed on a point where the building meets the sky giving the camera the best opportunity for a strong point.
As I’m using the back button to focus, I have disabled the shutter release button from performing its focus operation when it’s half pressed. In my mind having to half press the release button could affect my composition by possibly moving the camera a touch whereas the back button gives a different pressure on the equipment which makes it a little less likely it will move.
So how many focus points do you need, well, one and all of them, just not at the same time!