On 30 Oct 1998 16:33:27 GMT, laserandy@aol.com (LaserAndy) wrote:

>There is a trick (not really a trick) to figure out what f-stop to shoot for a
>certain depth of field if your lens has depth of field lines behind the focus
>ring. Focus on the closest thing you want in focus, and note where the focus
>ring lines up with the centerline of the lens. Then focus on the most distant
>thing you want in focus and note again where the focus ring lines up against
>the centerline of the lens. Now, turn the focus ring until each of the noted
>points lies opposite a depth of field line of the same color. Choose the
>f-stop which corrosponds with that color (or a higher numbered one) and shoot
>the picture without adjusting the focus.
>
>The lines represent what will be in focus for a given f-stop. They get wider
>and wider as the lens gets shorter. On the 135mm I'm looking at, 68' to inf.
>can be in focus at f16, whereas, on the 28mm I'm looking at, using the same
>f-stop, inf. to a little under 3ft should be in focus at the same time.
>
>The Cannon EOS (at least one I played with) had an auto feature to do this,
>where you focus on one thing, then on another, and the camera sets the f-stop
>to get both in focus (as the extremes of the depth of field). The method I
>described does the same for a man. focus camera.

That is the "official" way to use DOF scales, but there are problems
with that, I find... The standard chosen is not high enough, so the
DOF indicated isn't quite deep enough for the appearance of sharpness
over the whole range for critical use. Also, the more distant parts of
the photo, while technically equal in sharpness/unsharpness to the
near counterparts in the indicated DOF range, look less sharp. A
solution: after arriving at a focus distance and aperture using the
above method, fudge the focus a bit more toward infinity - then
check what new stop is required to cover the closest objects, and
stop down one additional stop. Assuming you have that stop available,
and that it is not too far into the diffraction range to be of use,
the results should be better than strictly following the DOF formula.