24mm f2.8 VFC

This is a MC 24mm f2.8 VFC lens. The VFC stands for Variable Field Curvature which changes the plane of focus, often called focus plane, from convex to straight (parallel to the lens plane and film plane) to concave.

With most lenses the focus plane isn't flat as commonly described in photography books but takes the shape of the outer lens element extended out to an infinite distance within the viewing angle of the lens. At some distance this essentially becomes a flat plane, but many lenses have been or are produced to have a flat focus plane.

This ensures what's in focus in the center of the lens is equally in focus at the edges. This is a necessity in macro and micro lenses where you want or need a flat field for the subject with wide apertures and narrow depths of field. The bulk of regular lenses are made with the curved focal plane with only some made with flat focus planes

The VFC technology, which was also adapted in the Minolta 35mm f2.8 CA-VFC lens, allows you to control the shape of the focus plane. This doesn't really change the large center area of the focus plane but changes in the outer edges to move the field of focus toward or away from the camera.

The asking price, shipping included in the US, is $500. You can get the full description of the whole Minolta system for sale.