P3D Re: Flash and 3D

[John Ohrt <johrt@xxxxxxxx>]

John W Roberts wrote:
>
> >The problem with on-camera flash is that light falls off very quickly as
> >distance increases.  (the inverse square law I think)
> 
> Therefore, purely on a mathematical basis and without having actually tried
> these, it would appear that:
>  - Using an extended flash (e.g. an umbrella reflector), the light should
>      fall off less rapidly than with a small flash source. [Inverse
>      square is the model for a point source.]
>  - If the flash is powerful enough, moving it back further away from
>      the subjects should help reduce uneven illumination (provided
>      the shadow of the camera, etc. doesn't fall on the subject!).


In effect, the flash source for the umbrella is a point source.  If you
include the distance from the source to the umbrellas surface in your
calculations, then the illumination level will obey square law.

However, the umbrella in effect is one way to achieve the secong method
of evening the levels of illumination over the scene, use a brigher
flash placed farther away.
-- 
John Ohrt *** Toronto, ON, Canada *** mailto:johrt@xxxxxxxx


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