focal length of a lens affect depth of field?
smaller focal length lens like a 28 mm on a 35mm camera is used there
is more areas of the images in apparent focus due to the increased depth
of field. Correspondingly with a longer focal length lens such as a
135mm on a 35mm camera the depth of field is very much reduced. when
using longer lenses the focus become critical. Also the lens may need
to be used on a tripod due to camera shake .
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.
Want to learn more? - do a workshop or one on one with Lloyd Godman