I just did a computation of DOF at 20mm with an f-stop of 22, and a
focal length of 1.1 feet (should be close to 14 inches-it wouldn't let
me use the inches number), and the computer told me that it would be in
focus from 8 inches to 2 feet 3 inches. Seems reasonably close to what
you need?
Here is the DOF calculator address:
http://members.home.net/gillettm/DOF.html
Mike
Jim Davis wrote:
>
> Tom, thanks for the answer, maybe you can give me some more info here.
> I want to focus a bit closer than the minimum focus, which is about 14
> inches. Which tube would give me, say 8-12 inch minimum focus? It sounds
> like I want autofocus, I think the 12mm tube would do what I want - possibly
> the 25mm tube would not allow me to focus far enough out. How close and how
> far out can the 25mm tube focus? I need a decent DOF from about 8 to 36
> inches. (That's about the length of a dog nose to tail mostly :-)
> Sorry not to email privately, don't have your address. In any case, this
> is definitely EOS stuff, maybe someone else is interested too.
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