F-number on reversed lenses

[LordV]

If I reverse a lens does the F-number mean the same thing in terms of DOF and diffraction. I assume it does not necessarily mean the same thing if the entrance and exit pupil are different ?

This question came up as someone thought the DOF of a reversed canon kit lens at a set aperture was thinner than other normally mounted macro lenses at the same set aperture and magnification.

Brian V.

[rjlittlefield]

For all lenses, the effective f-number means the same thing in terms of DOF and diffraction.

But lenses vary in how the effective f-number depends on the f-number that is set on the lens, especially when reversed and extended.

This does depend on the pupil ratio. See FAQ: What is "pupil ratio" and why would I care?

--Rik

[LordV]

For all lenses, the effective f-number means the same thing in terms of DOF and diffraction.

But lenses vary in how the effective f-number depends on the f-number that is set on the lens, especially when reversed and extended.

This does depend on the pupil ratio. See FAQ: What is "pupil ratio" and why would I care?

--Rik

Thanks for the answer Rik
Brian v.