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Yes, that'd be nice to see some more in depth explanation on what exactly causes diffraction at low aperture. My (wrong) assumption before was that a greater aperture, the incidence of light rays would be such, especially at the edges of the lens, to create high diffraction, but clearly there's something more complex happening while rays cross the various components of the lens.


The simple explanation of diffraction is that as light rays go through a small hole some of them get "caught" on the edges of the hole and bend around them and distort. Wikipedia can give a more technical explanation. That's why the smaller the hole (e.g. higher f number) the more diffraction effects you get.

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Oh right, I was assuming different focal length=>different aperture, but that's not necessarily the case. In other words, same aperture, same DoF regardless of the focal length...


Not quite. Same aperture + same magnification + same image format = same DoF. So a 50mm lens at 1:1 magnification has DoF equal to a 100mm lens at 1:1 magnification at the same aperture. So in Macro the choice of focal length only really affects working distance (100mm lens can be farther back from the subject at 1:1 mag. than 50mm).