Path: utzoo!utgpu!watserv1!watmath!att!att!rutgers!sun-barr!decwrl!sgi!donl@glass.esd.sgi.com
From: donl@glass.esd.sgi.com (donl mathis)
Newsgroups: comp.sys.sgi
Subject: Re: photographing the screen
Message-ID: <74073@sgi.sgi.com>
Date: 3 Nov 90 01:39:04 GMT
References: <26308.27257d14@kuhub.cc.ukans.edu> <1990Oct30.173541.14407@imax.com>
Sender: guest@sgi.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 44

In article <1990Oct30.173541.14407@imax.com>, dave@imax.com (Dave Martindale) writes:
> Some additional tips on exposure:
> 
> 1. If you have a spotmeter available, this is the most accurate way I know
>    to set exposure:  Plot a square of full-intensity white on the screen,
>    and read it with the spotmeter.  Then give the film 2.5 stops more exposure
>    than the spotmeter reads.
> 
> 2. If you don't have a spotmeter, but do have a through-the-lens meter on
>    your camera, fill the screen with white and take a reading, then give
>    2.5 stops more exposure.
> 
> [... other good advice ...]

Also, if you are using a digital meter, you may discover chaos in the
readings due to interaction between the sampling rate of the meter and
the screen frame rate.  I haven't measured our monitors, but i've
measured normal TV displays, and both of my digital meters have trouble
with them.  You might have better luck leaning toward an analog meter.

As to measuring white and opening up 2.5 stops, an alternative might be
to measure what you consider to be "middle gray", and just use the
reading directly.  In fact, if you want to get picky about it, you're
*really* looking for a black black and a white white, so you might want
to create a gray scale on the screen, covering the whole range, and do
some test shots of that to see how they reproduce.  If you find you
need to push the whites up a little higher, or the blacks down a little
deeper, consider having your E6 film push processed.  Conversely, but
much less likely in my estimation, if you lose some of the lighter
grays to white, or darker grays to black, consider asking for pull
processing to reduce the contrast of the film a bit.

On your test roll, bracket the exposures widely enough that you can get
all the exposure information you need on one roll.  Make your best
guess and cover it by, say, plus or minus four or five stops.  A roll
full of gray scale exposures should tell you almost everything you need
to know.
--

- donl mathis at Silicon Graphics Computer Systems, Mountain View, CA

donl@sgi.com

I want my Ektar sheets!