I found this in a box of stuff I was given: I think it is a shutter which fits on the front of a barrel lens. It has three settings: O - Permanently open for focusing. Z - Same as B i.e. shutter open whilst cable release is pressed. M - A fixed time release. In the M setting a fast press of the cable release gives a consistent open time of about 1/30 (rough guess). If the release is pressed slowly the blades will open slowly then snap shut. (the blades are shown half open in the picture intentionally with the control set half way between M and O). Can anyone tell me anything about this? Make, age, etc. Steve.