Good write up Don - I have been following it but I have been side tracked with a plumbing problem with my immersion heater - Any plumbing experts here !! Spent 2 days on it and the dam thing still not right !!
A couple of small points to add to this thread.
1) warning about putting old models of flash gun on digital cameras with a Hotshoe. Most of the older guns have a trigger voltage in excess of 200V which would fry the camera electronics.
Fortunately for me the Canon 20D has a Flash sync lead connection under the rubber flap rated at 250V.
2) As you have mentioned modern flash systems work on TTL metering basis. A number of these systems work by emitting a pre-flash (Canon E-TTL for example) to get some idea of the scene. Unfortunately the optical trigger units you illustrated attached to the remote flash are fired too soon by the pre-flash.
However there are a few new models of low power guns available for use as an optical slave which can be set to ignore the pre-flash.
Rob
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