On Sun, Jul 8, 2012 at 10:25 AM, Mark C <[email protected]> wrote: > ... I have never found a good explanation of what is going on when you reverse > mount a lens. After using reverse mounted lenses quite a bit, I can say that > reversing the lens allows you to focus closer. It also seems like the > subject to lens distance does not change as much as you'd expect when you > reverse mount and change extension. But I've never learned the theory.
It's a matter of how reversing a multi-element lens re-positions the lens' primary nodal point for light passing through the lens in the reversed direction. Perfectly symmetrical designs will reposition the primary nodal point symmetrically when the lens is reversed, but very very few SLR lenses are perfectly symmetrical. Reversing the lens in most cases not only reversed the lens elements but adds some extension due to migration of the primary nodal point. It's hard to calculate the shift ... -- Godfrey godfreydigiorgi.posterous.com -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
