To understand the principle of the baierfoto control device we should first have a look at the measuring roll in the Pentacon Six.
Function of the Measuring Roll in the Pentacon Six
What I call measuring roll is that device between film aperture and film take up spool. It is driven by the advancing film and should make film advance more reliable. But actually it often leads to overlapping of frames. Why?
Well, the effect of this device is only, to prevent film advance from going too far, while the uptake spool is becoming thicker towards the end of the film roll. The device shortens the effective working angle of the advance lever, according to the measured length of film transport. This means, film thickness is automatically taken into account - 220 roll film with 24 exposures thus useable.
So far so good - But it is not possible for this device to make the working angle wider, that means: If advance is too short, it is not corrected and will produce overlaps in the rest of the film!
In addition in some cases the mechanism produces malfunctions itself, causing overlappings - as we saw, for the rest of the entire film.
This Pentacon device will not give perfect control of film advance without some help. The baierfoto film advance control unit is that help:
We should now have a closer look at the mechanism of that measuring roll in the Pentacon Six:
Cog 11 is connected to the end of the measuring roll. It drives shifting wheel 9 clock-wise. Due to the gear-ratio, one turn of wheel 9 is reached just when the film has driven the measuring roll 55mm (width of frames is 54mm).
Lever 8 is lying on wheel 9 with the pull of a spring.
When the gap in ring 9 reaches the little cam on lever 8, this would fall into the gap (because of the above mentioned spring tension). In its starting position shown in the drawing, the lever is prevented from falling in by leaf-spring 10. After one full turn, the leaf-spring is pushed aside by the cam on lever 8, which then falls in. If this is the case before the end of the advance lever´s way, the advance mechanism is set to shorter for the following frame . (Because more than exactly one turn of wheel 9 means, advance is too far). (Fatal misfunction possible...)
When the shutter release button is pressed, lever 8 is lifted out, and leaf spring 10 snaps in again. Thus lever 8 is prevented from fallig in, until the next full turn is reached.
We can now understand, that it would be very useful to know the position of lever 8 during film advance. This is exactly what the baierfoto film advance control device lets you do!
Red is equivalent to lever 8 out
Green is equivalent to lever 8 in
Thus the control device is capable to give us the infaillable information: Film advance is enough - or not! We now control advance as follows:
Before shoooting the display shows green.
After shooting it shows red.
We advance film, until the display shows green again. If it does, when we lead back the advance lever, we know the film has advanced at least 55mm. If it does not, we let the lever back part of the way and push it towards the end again until we see green, that´s it!
We can be 100% sure that advance was enough, for wheel 8 cannot make one entire turn unless the film has moved the correct amount!