[photo-3d] Re: externally twinnables & flash

[JNorman805@xxxxxxx]

Peter Davis writes:

<< Does this mean you can put a flash on one camera, and both are sync'ed 
well 
 enough to get the light?>>

Yes.

<<How does the second camera's auto-exposure "know" 
 there's a flash? >>

It doesn't.  For flash, I go into manual exposure mode:
    Step 1.  With the cameras still in aperture priority mode, I set the 
aperture that I want (f 11, for example).  Then I press the button down 
halfway to activate the metering system in both cameras, and check to see 
what shutter speed it wants without the flash.  Presumably, if I am 
contemplating the use of flash, it'll be slower than the camera synch speed 
of 1/90 sec.  If it's not at 1/90 or slower, I choose a smaller aperture.  So 
far, this is just basic flash-fill technique.
    Step 2. I set the Vivitar 285 for aperture I want with the speed of the 
film I am using.
    Step 3.  I put the cameras on manual exposure mode (but leave the lenses 
in autofocus mode), and match the apertures of both cameras to the aperture 
indicated on the Vivitar 285 autosensor.  I set the shutter speeds of both 
cameras to the speed indicated by my earlier exposure check (if I want full 
ambient light in background areas that are not reached by the flash).  If I 
don't want full ambient light, I set the shutter speeds faster than what the 
exposure check told me (but of course never faster than the camera's rated 
synch speed).
    Following the above steps doesn't require that either camera "know" 
there's a flash.  It's just that the flash fires within the rated synch speed 
of both cameras.  As a general rule, I try to use shutter speeds at 1/30 sec 
or slower when I'm using flash.  I can't explain why, but that increases my 
success rate dramatically.  Even so, every once in a while, the two cameras 
will not fire at the same instant, creatingt a dark band across the image 
that was produced by the camera that didn't have the flash mounted on it.  
For the most part, though, the two cameras really do fire in precise enough 
synch so that both get flash coverage.

Jim Norman