The Praktica Shutters

Comparison of the Praktica MTL3, BC1, BX20 shutters.

These three shutter are seen from lens side.

The shutter of the MTL3
The control drive does not appear, because it is fixed on the mirror-block. Not easy to make it work alone, because when it is not fixed inside the camera, the blades can fall.
The main characteristic of these Praktica shutters is that they use 3 blades (in fact 6 of them, 3 for each curtain) this shutter is rather cumbersome, since the place for these 3 blades is necessary in top and bottom when the curtains are open (during a release, the top curtain goes up to open the window, the 2nd curtain (at the origin folded in the lower part) is released after a time corresponding to the programmed exposure time (for times lower than the flash-synchro one, this 2nd curtain is released before the first is fully opened) when the shutter is cocked again, the two curtains go back down together.

The shutter of "B" series
How to make a 3 blades shutter fit in a very compact camera? Well, by making the higher blades pass in the eyesight during the release! thus, the sequence is modified: the curtains go down again together at the end of exposure, and when cocking the shutter again, only the springs which control the 2 sets of curtains are bent.
This shutter is electrically controlled: an electromagnet (it is missing on this shutter, I materialized it by a blue rectangle) retains the second curtain for a time corresponding to the exposure. For the flash exposure, the 2nd curtain is released when a switch indicates to electronics that the first curtain is open. Without battery, you believe you're exposing, since the shutter sounds, but the 2 curtains move simultaneously, no light passes through.

The shutter of the BX 20
The 3 blades were let down for a more traditional and compact 4 blades (which does not come any more to hide the sight).
There are two electromagnets, I suppose one for each curtain (you can guess 2nd one in top on the left) without battery, it works like a “B”, without exposing.