I have a late 70's Caltar version of that lens (so they told me). It has a slider "knob" on the lens barrel. The cocking lever is near the top on the leftr as you face the lens from the subject side. This knob, kind of triangular shaped (thumb and forefinger fit nicely into the sides), is on the right side about halfway down from the top. You just slide it around the barrel to open or close the shutter, no matter what the speed is set on - very handy. My other two lenses have a similar device, I would suspect yours does too.