AF points - some questions

[gary-s]

I'd like to know if there is any real difference between using the center only AF point and using all of them. I mostly use just the center one for things such as sports so i can follow something easily, but for general still photography, should i really be changing it?

edit: i guess im really asking for an explanation on how exactly the AF points affect the image :)

[toxic]

The center point receives the most light, so it is the most accurate. It is probably your only choice for reliable AF in very low light, especially with your camera, which has a cross-type point in the center and single-line points everywhere else.

The outer points in your camera are useful with decent light and are best used when you can't afford to have DoF shift from focusing with the center and recomposing. This is most frequently an issue with close portrait work.

[KCMO Al]

Yes, the center point is the most accurate, particularly on the 5D. It's all I ever use. I like to focus and recompose so it's not a problem.

[DStanic]

More so with longer and high-aperture lenses (85 f/1.8 for example) using one of the other focus points can me more accurate then using the center and recomposing. I still use center most of the time for general stuff.

[Veemac]

if you're talking about using Auto AF Point Selection vs. manually selecting the center point, I can't think of a situation where I'd ever use it. The camera has no idea which point in the picture you have in mind as the focus point, so it will make an "educated guess" - which may end up being nowhere near what your intention was.

Manually selecting other points, OTOH, is a good idea depending on the composition of your image (i.e., if what you want to focus on is on the right side of the picture, select the focus point closest to it.)

[lettershop]

are the AF points on a separate sensor? or are they on the same sensor used for the camera image?

[gary-s]

So if you have all the AF points on, is it just ONE AF point that focuses anyway?

[Veemac]

So if you have all the AF points on, is it just ONE AF point that focuses anyway?
The camera may show more than one, but they'll be on the same focal plane regardless. It doesn't change the fact that a camera can only focus on one focal plane at a time. The difference is that you don't get to choose where it's focusing.

[Jon]

are the AF points on a separate sensor? or are they on the same sensor used for the camera image?
They're on a separate sensor, at the bottom of the mirror box.