The Zeiss, like the huge majority of ~50mm lenses in existence, is a so-called Double-Gauss design [1] (yes, that Gauss [2]). The role of the interior doublet i

The Zeiss, like the huge majority of ~50mm lenses in existence, is a so-called Double-Gauss design [1] (yes, that Gauss [2]). The role of the interior doublet is mostly to reduce aberrations, so reversing it basically has the opposite effect (at least spherical and chromatic aberration appear to go crazy). Would be interesting to see some raytrace diagrams of the modified lens. [1] https://en.wikipedia.org/wiki/Double-Gauss_lens https://en.wikipedia.org/wiki/Double-Gauss_lens [2] https://en.wikipedia.org/wiki/Carl_Friedrich_Gauss https://en.wikipedia.org/wiki/Carl_Friedrich_Gauss