"...you may want to just pre-set the aperture, to a larger number..."
I agree....
Actually, first be sure you are using a relatively wide angle setting on the lens (I'm assuming it's a zoom). Wide lenses naturally have greater depth of field that will help keep much of the area encompased in the image in focus. Ultrawide lenses such as Canon 10-22mm, at its wider end, or even wider "fisheye" lenses hardly need to be focused at all... DOF is so deep. But an 18-55mm lens set to 18mm will also give fairly great depth of field.
Nextbe sure to select a small aperture (a higher number).... for example, use f/8 or, better yet f/11. These smaller apertures will get you maximum depth of field possible with the lens, yet aren't so small that "diffraction" starts to become a problem. (You can test f/16 and f/22 to see if they meet your purposes, but watch ouf for loss of fine detail in your images, at such small apertures.)
I'd still go ahead and focus the image, as per above recommendations. Be sure the camera is in One Shot mode, so you get Focus Confirmation. Hopefully you'll be able to hear the "beep" when focus is achieved. Focus in Live View mode is rather slow, so the confirmation might be important.
There are Depth of Field charts and online calculators. Another thing you might want to study up on is "hyperfocal focusing distance". Between these two, you'll know better how to get a pre-planned shot fully in focus.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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