AF points and F/stop - sharpness

[Undiscovered]

Camera: Canon XT

Say I shoot at F/5.6 and manually select the AF point be on the far left so that area is in focus and the rest is in blur, when I up the f/stop to say f/11,16,22 does the AF point even matter at those depths?

What i'm trying to acheive is is sharp looking pictures close up. Say I'm 8 feet from my subject, but want the entire photo to look sharp, by using F/5.6 the subject will remain in focus, but the rest of the shot will be blurred, but by using a higher F/stop (say F/16), shouldn't the entire photo be sharper? Is this the only way to have the entire picture in focus, by only using a higher f/stop, regardless of how close I am to the subject and not to worry about the AF point? or can an entire sharp photo be achieved with a lower f/stop?

Thanks

[droiby]

If you want to have the entire scene from foreground to infinity to be in focus, then you've got to be prepared to stop down to something small (high F-numbers). It also wouldn't hurt to read up on hyperfocal distances as well, to maximise your DOF.

[jnick]

In cooperation with stopping down to say, f/22, couldn't you also use every AF point, instead of just one?

[StewartR]

Say I shoot at F/5.6 and manually select the AF point be on the far left so that area is in focus and the rest is in blur, when I up the f/stop to say f/11,16,22 does the AF point even matter at those depths?Yes it does matter, unless you're using a wide-angle lens.

Try playing around with a Depth Of Field calculator such as the one at DOFMaster.com (http://dofmaster.com/dofjs.html). I don't know what kind of lens you have, but let's look at how the 18-55mm kit lens works, with a subject distance of 8 feet:

Focal length 18mm
f/5.6 : DOF from 4.44 feet to 40.6 feet
f/8 : DOF from 3.75 feet to infinity
f/11 : DOF from 3.07 feet to infinity
f/16 : DOF from 2.45 feet to infinity
f/22 : DOF from 1.9 feet to infinity

Focal length 28mm
f/5.6 : DOF from 6.01 feet to 11.9 feet
f/8 : DOF from 5.45 feet to 15 feet
f/11 : DOF from 4.82 feet to 23.6 feet
f/16 : DOF from 4.14 feet to 122.4 feet
f/22 : DOF from 3.45 feet to infinity

Focal length 55mm
f/5.6 : DOF from 7.38 feet to 8.74 feet
f/8 : DOF from 7.14 feet to 9.09 feet
f/11 : DOF from 6.84 feet to 9.63 feet
f/16 : DOF from 6.45 feet to 10.5 feet
f/22 : DOF from 5.98 feet to 12.1 feet