The F auto Topcor lens series (3,5cm, 5,8cm, 10cm and 13,5 cm) had an fully automatic diaphragm. These lenses are the forerunner of the RE-auto Topcor lenses, but are not compatible with them due to a design difference.
These lenses were mounted on the Topcon RII and RIII and Topcon RS camera which have a lever on the body to open or closed the diaphragm to the preset setting. On shutter release they close fully automatic to the preset setting. Hence the name F (fully) auto Topcor. The aperture lever on the lens is however not compatible with the TTL system of the Topcon RE Super, as it works reverse to the RE Auto Topcor lens series. These lenses have a unique modern design for the first time rubber rings were used to enhance focus grip, and the lens had a very modern display of the focus and diaphragm settings on the lens-barrel behind transparent plastic
Like the Topcon RS camera the F auto Topcor seems a ‘forgotten” item. Next to them also a F H auto Topcor lens series should have been appeared on the market (see website Topcon club).