Soligor funky FD mount?

[SOVERN]

Just bought a Soligor 75-205 zoom lens for my Canon Ae-1P. The shutter-mirror doesn't fully expose when this lens is attached, unless I push in the "stop-down lever." I can also take photos with the stop-down lever engaged but in the manual it states that when shooting with the lever engaged the exposure may not be correct. For those who are unfamiliar, the stop-down lever is used for metering. Here is a picture of the lens mount, and a picture of my 28mm vivitar lens with a proper FD mount:

(above) Soligor 75-205mm with funky FD mount.
(below)Vivitar 28mm FD mount.

 

[Mitica100]

"Canon had four breech mount variations: 1) the original R mount for the 1959 Canonflex 2) the FL mount which used stop down metering 3) the FD mount which used open aperture metering and 4) the "bayonet" mount modification of 1980 introduced for quicker lens changing. Types 1, 2 and 3 are identifiable by the R, FL, or FD designations on their filter ring. Type 4, sometimes called FDn by its admirers, sometimes called not so nice names by its detractors, is identifiable by its black plastic mount which rotates the lens on and off the camera, rather than rotating a metal breech lock like the previous versions. These later lenses sometimes have plastic barrels which the earlier lenses did not. Personally I prefer the last mount due to it's MUCH faster lens changing. Purest claim the earlier mounts are better made and stronger...some even going so far as to pay a premium for those lenses. While the R mount lenses have the same breech mount and back focus, their internal mechanics will not mate with later cameras to offer either metering or auto-diaphragm operation. Be careful mounting R lenses to later camera bodies...you may damage your camera, or lens, or both."

Read here.