P3D Re: Vivitar 283/285

[Brian Reynolds <reynolds@xxxxxxxxx>]

John Ohrt wrote:
> 
> I have this mechanical Russian copy of a Zeiss.  It has a hot shoe and a
> connector for the cable.  I can see how it knows that the shutter has
> been activated, but how can the flash automatically assess proper
> illumination?
> 

There are two methods of flash power determination.  The obvious one
is manually setting the flash power.  The automatic modes involve a
light sensor connected to the flash and telling the flash the exposure
settings for the camera (either with a "calculator" on the back of the
flash, or through electronic contact points on the hot shoe for
flashes made for specific camera systems).  The light sensor reads
light reflected back towards the camera during the exposure.
Electronics in the flash cut off the light output based on the
exposure settings.  This can have the added benefit of making the
recycle time between flashes shorter (since the entire charge was not
used).

-- 
Brian Reynolds                  | "Humans explore the Universe with five
reynolds@xxxxxxxxx              |   senses and call the adventure science."
http://www.panix.com/~reynolds/ | - Edwin P. Hubble


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