> Oops,
>
>
> Should have been 3 stops, not 9.
>
>
> Dick
>
> <center>
>
> Bostick & Sullivan
>
> Http://www.bostick-sullivan.com
>
> 505-474-0890 FAX 505-474-2857
>
> </center>
>
OK, I know its just numbers, but inverse square says when you double the
distance, you need four times the exposure. Going from 3 inches to two
feet (24 inches) is eight times the distance. Eight squared is 64, so you
should need 64 times as much exposure, if it were a point source. Or you
can look at it this way; from 3 inches to six inches, the exposure is
multiplied by four. From 6 to twelve it is multiplied by four again, or
16 times the original. From 12 to twenty four inches, four times again,
or 64 times the original exposure. Six stops, yes?
Same basic conclusion, diffusion banks do not act like point sources at
close range.