The 135mm is most commonly found as Adapt-A-matic Interchangeable Mount, but was also made as a fixed mount, and as the first version adaptall 135mm. And in fact that lens' successor the CT135 is very similar in specification.There is also an uncommon and relatively undocumented f3.5 version, later style with rubber focus grip rather than original milled grip (pic 2 - courtesy Luis Alegria).135mm F/2.8Optics: 4 elements in 4 groups58mm filter1.5m close focusing9 Blade apertureLength: 3.5" (89mm)Weight: 14.6 oz. (415g)Solid metal buildBuilt-in HoodAuto-Manual SwitchRead more at: https://www.pentaxforums.com/userreviews/tamron-135mm-f-2-8-auto-adapt-matic-mount-jsg-28au.html#ixzz794RUxElq