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[OM] Re: E300 to studio flash

Subject: [OM] Re: E300 to studio flash
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Tue, 21 Nov 2006 07:12:33 -0500
An ISO compatible hot shoe has the flash trigger contact in the center 
and a "ground" connection in the groove at the side of the foot.  The 
trigger contact is also usually larger than any other contact.  Power to 
this contact comes from the flash unit itself.  The camera's job is 
simply to throw a switch to complete a circuit back to the flash's 
"ground" contact and cause the flash to fire.  A PC connection on the 
camera provides those same two electrical connections to the flash via a 
two wire cable.  A trigger voltage on one wire and "ground" on the other.

What happens after the flash is fired is a function of all those other 
contacts that might be sprinkled around the trigger contact that allow a 
modern flash and camera to communicate.  But what all those other 
contacts do is proprietary to camera and flash unit and almost never 
compatible even between different camera lines from the same manufacturer.

Since the power to operate the flash comes from the flash itself you 
need to be aware of the voltage applied to the hot shoe or PC contact by 
the flash.  Old cameras with mechanical switches (like the OM-1) don't 
care if you slip them a couple hundred volts.  Cameras like the Canyon 
10D and 300D, however, have dainty electronic switches as part of the 
shutter assembly and these can get fried by voltages much above 6 volts. 
  Old studio flash units like old portable flash units can have voltage 
levels measured in hundreds of volts.

Studio flashes have no smarts at all other than most have some ability 
to manually vary the power output.  Some are quite simple and only allow 
varying power over a couple discrete steps with one or more switches. 
Fine tuning the light level must be done by varying the flash distance 
to subject.  Other units have continuously variable power.  My Alien 
Bees are steplessly adjustable over a 5 stop range.

Chuck Norcutt

James Royall wrote:

> The answers got more and more detailed. Thanks, I now understand  
> completely. I didn't realise that there would be a contact in the  
> same place on all hotshoes - seems far too easy.
> 
> James



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