Canon FD 28mm S.C. f2.8 Lens

From the Canon Camera Museum;

This is a wide-angle FD lens developed with emphasis on high performance and ease of use such as resolution, contrast and color balance.
Increasing the performance of a wide angle lens generally leads to an increase in overall length, but the FD28mm f/2.8 S.C. resolves this issue through appropriate power positioning of the optical system. This offers high performance satisfying requirements for enlargement of highly magnified images and detailed definition, while also succeeding in reducing size.
(I) and (II) are different in their locking mechanisms of their aperture levers. In (I), the aperture lever is fixed in position after it is rotated counterclockwise to its maximum. On the other hand, in (II), the aperture lever is fixed after it is rotated counterclockwise to its maximum and further the clamp is set at the “L” sign.