Sunagor 500mm "telescope"

I have the above lens but have not been able to find anything about it on the web. My question is: -
It has a standard manual focus, then moving towards the camera it has variable aperture f8-f22 ring. Next is a ring which has O C. This interacts with the apeture ring when moving from O to C in that it pushes the aperture from f22 towrds f8.
Any idea what this is or does?
Not sure I'll get any decent photos with it - Not convinced it is any good.....anyone used one?
Cheers
Donut

You set the aperture to the desired value and then focus when it's (O)pen, then (C)lose it down to actually take the photo.

Never used one though, it'll be interesting to see your results.

Cheers hefty1.
That explains it
Donut

Sunagor made some decent lenses in the mid 70's. They made the 1st 135mm I ever had that focussed to 3ft, very good optically, but the twin screw focusing system they used eventually jammed up solid.

shim