Xref: utzoo comp.sys.ibm.pc:26245 rec.photo:4960
Path: utzoo!utgpu!watmath!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: comp.sys.ibm.pc,rec.photo
Subject: Re: Photographing PC Screens
Message-ID: <17769@onfcanim.UUCP>
Date: 15 Mar 89 01:29:13 GMT
References: <3779@peora.ccur.com> <3939@kuhub.cc.ukans.edu> <7454@pyr.gatech.EDU>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Followup-To: comp.sys.ibm.pc
Distribution: na
Organization: National Film Board / Office national du film, Montreal
Lines: 16

In article <7454@pyr.gatech.EDU> curci@stat.fsu.edu (Ray Curci (scri)) writes:
>Use the video screen
>as your light source (no flash), and when you measure the light do it
>from the camera's location because of the inverse square law will give you
>misleading readings especially at close range.

This is just plain wrong.  You do need to fill the light meter's field
of view with the image (so you aren't measuring the black area outside
the screen), but other than that the distance just doesn't matter.

The intensity of light from a particular point on the screen does fall
off with the inverse-square law, but the area of the screen being
measured increases as the square of the distance between the meter and
the screen, so the two effects cancel out.  This is the same reason
that the correct exposure for an object does not depend on distance
from the camera (unless you are doing macro photography).