# 16. If I focus on some point, and then recompose with that point not in the center, will the focus be off?

## Description

This article is from the
Photographic Lenses FAQ, by David Jacobson with numerous
contributions by others.

# 16. If I focus on some point, and then recompose with that point not in the center, will the focus be off?

Yes, but maybe only a little bit. If the object is far enough
away, the depth of field will cover the shift in distance.

An approximate formula for the minimum distance such that the error
will be covered by depth of field is given by

d = w^2/(2 N c)

where

d = minimum distance to make the point be sharply rendered
d is measured from the film plane

w = distance image point on the film is from center of the image

For the 35mm format w^2/(2 c) is 5.4 meters, so you can recompose the
image with the subject at the edge of the frame and still have it be
sharp if the subject distance (at the center) was at least 5.4 meters
(18 feet) divided by the f-number. See the technical notes at the end
for a bunch of assumptions.

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