Flash trigger question.

[BIG4D]

Hi all. I hope someone can give me some insight here.

I am curious how exactly a hot shoe triggers a flash. I know there are several connections on the shoe itself, but from what I have read, there are actually only 2 terminals that actually trigger the flash to "fire". The rest are for metering and automatic zoom capabilities.
What does the camera do with these two terminals to make the flash "fire". Does it connect them together? Does it apply voltage to one or both of the terminals?

i am trying to come up with a flash trigger that fires the flash when something crosses a beam of light. I have a schematic but the flash trigger only has two connections.

BTW, I am working with a Canon 40D and 5D markIII

Any help is much appreciated.

[zona5101]

Originally Posted by BIG4D

Hi all. I hope someone can give me some insight here.

I am curious how exactly a hot shoe triggers a flash. I know there are several connections on the shoe itself, but from what I have read, there are actually only 2 terminals that actually trigger the flash to "fire". The rest are for metering and automatic zoom capabilities.
What does the camera do with these two terminals to make the flash "fire". Does it connect them together? Does it apply voltage to one or both of the terminals?

i am trying to come up with a flash trigger that fires the flash when something crosses a beam of light. I have a schematic but the flash trigger only has two connections.

BTW, I am working with a Canon 40D and 5D markIII

Any help is much appreciated.

I believe it simply closes an open circuit to ground. IIRC, it is the center pin and a contact at the shoe wall. All the other remaining pins surrounding the center pin on the top of the shoe are for other data sharing functions.

[theArchitect]

Pocket wizards only connect to the centre pin so I guess that's all that's needed for a trigger.

[BIG4D]

Yup, that is all it took. Played with it tonight and it worked great. Thanks.