Full Frame Sensors Have More Bokeh? Think Again...

I have heard it at least a zillion times in photography forums and in some articles, "If you want more bokeh, go full frame..." I have always accepted this to be the ultimate truth although all it takes is a few seconds playing around with a DOF calculator and one would be confused as hell.

Yes, the DOF calculators such as this one http://www.dofmaster.com/dofjs.html would produce results that contradicts this notion, at least as I interpret them. All this while, I always thought that I was merely misinterpreting or misunderstanding things and that FF sensors would produce shallower DOF and more Bokeh.

Then I came across this from Bob Atkins. It is the 5 Basic Truths of DOF

http://www.bobatkins.com/photography/technical/digitaldof.html

1. For an equivalent field of view, a Canon APS-C crop sensor camera has at least 1.6x MORE depth of field that a 35mm full frame camera would have - when the focus distance is significantly less then the hyperfocal distance (but the 35mm format needs a lens with 1.6x the focal length to give the same view).
2. Using the same lens on a Canon APS-C crop sensor camera and a 35mm full frame body, the a Canon APS-C crop sensor camera image has 1.6x LESS depth of field than the 35mm image would have (but they would be different images of course since the field of view would be different)
3. If you use the same lens on a Canon APS-C crop sensor camera and a 35mm full frame body and crop the full frame 35mm image to give the same view as the APS-C crop image, the depth of field is IDENTICAL
4. If you use the same lens on a Canon APS-C crop sensor camera and a 35mm full frame body, then shoot from different distances so that the view is the same, the Canon APS-C crop sensor camera image will have 1.6x MORE DOF than the full frame image.
5. Close to the hyperfocal distance, the Canon APS-C crop sensor camera has a much more than 1.6x the DOF of a 35mm full frame camera. The hyperfocal distance of a Canon APS-C crop sensor camera is 1.6x less than that of a 35mm full frame camera when used with a lens giving the same field of view.

If you take a look at point 3 (in pink), you would realize that it is obvious. Why? Because nothing has changed for the lens in real life. All an APS-C sensor does is to crop. Something that you can do in post processing as well, in fact we all do it most of the time.

So you open an image in Photoshop, do some cropping, and voila the DOF changes? Ofcourse not! That is precisely what APS-C sensors do - cropping.

Why DOF is seen as shallower for FF sensor is because of point 4 (in blue). Photographers need to get closer to the subject to get the same angle of view. In many of the so called bokeh test, the distance to subject is not constant. As an FF camera gets closer to the subject to get the same angle of view as an APS-C camera, the DOF decreases and the bokeh increases.

Makes sense? At least this seems to be the most logical explanation of all the confusion I had with APS-C, FF, DOF, Bokeh, man, women, Tax Filing, etc.... well, at least it solved the first four things for me... :D