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I usually find, after blowing up my pic on the computer, that at one point (where I wished to focus) the image is very sharp, then as I inspect the picture I see that some more parts of the image, either horizontally or vertically, are in focus.
My confusion is that when we lock the focus at a certain point, is it that entire plane (both in the x and y directions) that is in focus? because I see most of the time (in Macro), that focusing is either horizontal or vertical or am I mistaken, because of minute differences in distance? E.g.,
(In focus) | | (Not in focus ) ________|__________ (Not in focus or I have mistaken) | | | (In focus)
I understand the general statement that a higher F-number means a greater area of focus.