I found prewar FED 1 with interesting shatter button. I’m not sure if this FED originally sold like this? Or this is optional part made by FED? Or may be it home made? Or made by/for Leica outside the USSR? http://www.ussrphoto.com/UserContent/DSCF6955.JPG
Yes, this button was found on FED 1B. I was able easily unscrew this button and under it I found standard shatter button. Sorry for bad pictures - Webcam :) http://www.ussrphoto.com/UserContent/DSCF6957.JPG