Canon 5d Mark iii Help with focusing

With all due respect, and I say this as cautiously as possible, you need to take some classes in photography.  It's apparent from your first two or three comments that you don't really have a firm grasp of the mechanics of photography.

If you change your aperture ("f number") you need to change your shutter speed, too.  Without seeing any of the images you're having problems with, it's difficult to form a good answer on what, if anything, you're doing wrong.  But the first thing I'd do, if I were you, is sign up for a basic SLR photography class.

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Skip M
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