[stevebrot]

When the shutter is fired, and after it is fully open, a voltage free contact (*) in the camera closes (or semiconductor device goes to on state) and if a flash is connected, pulls the centre pin to common (common being the rail of the hotshoe mount or the outer of the pc socket).

In the old days that allowed the current from the battery to ignite the flash bulb.
With an electronic flash, the tube is ionized when the center pin is pulled low.

Thanks for the detailed explanation with appropriate terminology. It may not be clear, but the current to ignite a flash bulb comes from the flashgun battery, not the camera body. The hot shoe is only "hot" when it has a flashgun mounted and even then only when the gun is turned on. Your comment regarding the ability of a multi-meter to detect continuity across the shoe contacts at short exposure times is quite true. Fortunately the switch remains closed for the duration of the exposure with most focal plane shutters. The leading curtain closes the switch and (with most*) the trailing curtain opens it. That is why I suggested a longer shutter speed to test the circuit.


Steve

* My Soviet rangefinder cameras leave the circuit closed until the shutter is cocked. As a result, the flash battery can drain rather quickly if you neglect to wind on.

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Last edited by stevebrot; 07-15-2015 at 02:04 AM.