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Figure 2-4. Shutter blade unlatching action
To synchronize flash circuit firing with the instant of maximum shutter opening, the
Wheel driving the Shutter Blade has a cam lobe on its lower edge (Figure 2-5).
Figure 2-5. Wheel cam closure of X-sync Contacts
As the Wheel rotates under spring force to spin the Shutter Blade, this cam lobe forces
the upper X-Contact against the lower X-Contact, closing this switch.
But because the cam lobe also momentarily closes the X-Contacts again on its return
travel, a means must be provided to prevent a second flash firing. A microswitch
Release Lever
Shutter Blade
Wheel (Spring-coupled
to Pressure Lever)
Pressure Lever
Normally-Open Contacts
Wheel Latched
Contacts Closed by Shutter Release
Wheel Unlatched
Wheel
Pin
Lower Contact
Leaf B
Upper Contact
Leaf A
Plastic Screw
0.5mm
Cam
Lobe
