[photo-3d] Flash guide number calculations

[Ralph Johnston/Linda Sherman <copley@xxxxxxxxxxxxxxx>]

The calculation is correct.  The guide number doubles for every x4 in ASA or
two stops on the diaphram.  This is because if the object distance doubles,
four times the light is required.  -Ralph




>
> Message: 19
>    Date: Thu, 6 Apr 2000 22:15:03 -0600
>    From: Bob Wier <wier@xxxxxxxxxxxxxxxxx> 
> Subject: GN 
>
> I am looking at the manual for an older flash unit.
>
> It says:
>
> GN 50 ASA 25 DIN 15 in feet
>
> Am I correct in thinking this indicates a GN of 100 for
> ISO 100 speed film?
>
> Thanks!
>
>               Bob Wier


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