Quote Originally Posted by Daniel Browning


Once you've decided on a composition, there is no way to get deeper depth of field except by using a narrower iris diameter (i.e., stopping down). [There are some hard ways, such as using a tilt-shift lens or focus stacking.]


If you move forward and zoom out (to get the same framing), the DOF will remain the same.


If you move backward and zoom in (to get the same framing), the DOF will remain the same.


So moving doesn't really affect the DOF. However, it does affect the perspective and background blur. Further away + longer focal length = flatter perspective and more background blur.


So I chose to pull out my handy-dandy iPhone and bring up DoF Plus. It's set to the Canon 40D at the moment.


Field of view, 35mm at 10m to subject, is 6.32m wide by 4.21m high.


Field of view, 70mm at 20m to subject, is 6.32m wide by 4.21m high.


Depth of field, 35mm at f/4 (8.75mm iris) at 10m to subject, is 6.17m to 26.19m (-3.83m and +16.19m).


Depth of field, 70mm at f/4 (17.5mm iris) at 20m to subject, is 15.27m to 28.94m (-4.73m and +8.94m).


Depth of field, 70mm at f/8 (8.75mm iris) at 20m to subject, is 12.35m to 52.38m. (-7.65m and +32.38m)


So, if I keep the same aperture, I get different DoF. If I compensate for iris diameter, I get double the DoF. I get the same numbers using the link found elsewhere in this thread. Am I mis-interpreting something? I'm not seeing the DoF staying the same with unchanged iris diameter.