Depth-of-Field (DOF) Preview The depth-of-field or in other
words - the distance range which is covered by the in-focus
field - is dependent on the object magnification. Object
magnification = size of the object on film compared to the real
world. e.g. magnification 1:100 = the object is 100 times bigger
in the world than on film. 1:100 would be e.g. a full body
portrait (=18mm on film -> 18mm * 100 = 1.80m for a person in
the real life). At magnification 1:100 you have a smaller DOF
than at 1:1000 and a bigger DOF than at 1:10. Stopping down to
e.g. f/8 has a different effect on the DOF - it increases but in
increases by a different degree. At 1:1000 this may cause the
DOF to cover everything in the scene (foreground to inifinity
distance). However, at 1:10 you have increased you DOF by just a
few centimeters (the background is still blurred). And this is
the sense of the DOF preview button - because the effect on the
DOF is different dependent on the object magnification it offers
you the possibility to PRE