P3D Re: Flash Cluelessness

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Many questions from Michael Georgoff regarding flash...

It is very easy to understand flash.  First, understand the manual
mode, which means that the flash fires with all it's power (and
longest duration).  This is a constant light output.  Depending
on your distance of your main subject, you set the aperture
accordingly.  The product of distance x aperture is constant as
BobH noted.  This is the guide number of the flash.

In auto mode the flash will fire a fraction of it's power, up to
full power, depending on the scene.  A sensor in the flash 
mesures the amount of light and stops the flash when the exposure
is correct for the given scene, up to maximum power.  To get the
smallest duration you must use the minimum amount of power (light
output) that the flash is capable of.

Since your flash is pretty weak and you are inclined to use
small apertures (but why use f16 for DOF reasons when there is will
be no light far away?) it is better to use the flash in manual
mode.  Then you will get its full ouput and you decide on the
camera aperture setting, based on the distance of your object.

-- George Themelis



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