As a camera with the
same focal length lens and set at the same aperture is moved further
back from the subject in focus, the depth of field also increases.
To gain significant depth of field when doing close up work
therefore requires more critical attention to the lens selection,
aperture and critical point of focus. Also
if we retain the same camera position, keep the same aperture and
alter the point of focus the depth of field has a significant effect
on the resulting image.
Again, note that there is less depth of field closer to the camera
position from the point of focus than in the distance. Remember to
allow for this by focusing on a point closer than mid way, about 1/3
to 2/3 is the general rule.
this series of images show the point of focus moved to illustrate
this - in first image on the left, we see the camera focused on the
twig and shoot in the top as the subject - nearly all of the interwoven
branches behind fall out of focus. In the second in the centre, the
subject becomes the twig in the centre - by moving the point of focus
further from the lens of the camera, notice how the image, has all
but disappeared. In the last image on the right, the point of focus
i much further back and there is a greater depth of field.