Ahh, now were gettin somewhere. Gravity shutters,great idea, I'll throw that in the sketchbook.
Donald-you seem to be smellin what I'm steppin in. Rotary with a spring or two with one speed and B. Thin brass circle with a hole in it etc.... This is what I originally had in mind and I was looking for maybe a picture of what someone else has done. I found pictures of a Holga shutter, I have a Kodak with a shutter like I'm talking about but I cant get the thing apart without damaging it and it works so I'm going to leave it alone.
Great ideas-keep em comin.