Simple explanation of the effect of aperture on DOF?

[KmH]

What does model size have to do with it?

As focal length changes, if model size (scale) in the frame is kept constant, so to is the DOF kept constant, because by maintaining subject scale as focal length gets longer or shorter, the focus point distance gets closer or farther from the camera.

 

[Helen B]

As focal length changes, if model size (scale) in the frame is kept constant, so to is the DOF kept constant, because by maintaining subject scale as focal length gets longer or shorter, the focus point distance gets closer or farther from the camera.

That only holds for near subjects. The lower the magnification and hence the closer the short lens comes to being focused at its hyperfocal distance, the greater the DoF of the shorter lens in comparison to that of the longer lens.

Best,
Helen