Re: Preflashing film

[T3D Sam Wang <stmwang@xxxxxxxxxxxxxxxxxx>]

>Date: 	Thu, 22 May 1997 11:25:00 -0600
>From: T3D Greg Erker <erker@xxxxxxxxxxxxxx>

>Suppose I want to pre (or post) flash my film to
>reduce contrast slightly and bring out the shadow
>details. How best to do it?
>
>1) Probably the easiest way (if the camera is on
>the tripod) is to place a diffuser over the lens(es)
>of the camera and do a second exposure. Either stop
>down the lens more or use a ND filter with the
>diffuser.  Assuming no rapid changes in the scene
>you are photographing you will end up with a "flash"
>that is the average colour of the scene you just
>photographed. Is this good, okay, bad?  Is a white
>"flash" the best thing to do?

Since the flash exposure affects the shadows only, the color of light to
use depends on what's desirable for that region. Sometimes it is nice to
deliberately warm up the shadows and other times not.

--snip--

>How much preflash is desirable?  I recall the number
>of 5 or 6 stops below the exposure given to the film.

5 stops. Much more than that it'll lighten the shadows too much, and less
than that there would be hardly any visible effect.

The simple way to "pre-flash" is to point the camera at a piece of white
paper or cardboard, illuminated by existing light or electronic falsh.

Is it OK to get away from strickly 3D topics?

Sam

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Sam Wang                         e-mail: stmwang@xxxxxxxxxxxxxxxxxx
Art Dept - Clemson University     voice: 864/656-3924
Lee Hall, Clemson, SC 29634         FAX: 864/656-7523



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