Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rice!uw-beaver!uw-june!sloan
From: sloan@cs.washington.edu (Kenneth Sloan)
Newsgroups: comp.graphics
Subject: Re: HELP NEEDED IN PHOTGRAPHING SCREENS
Message-ID: <14739@june.cs.washington.edu>
Date: 29 Jan 91 01:39:40 GMT
References: <1991Jan27.232910.22575@ms.uky.edu> <1991Jan28.010515.708@vixvax.mgi.com>
Reply-To: sloan@cis.uab.edu
Organization: University of Alabama at Birmingham
Lines: 36

In article <1991Jan28.010515.708@vixvax.mgi.com> keeney@vixvax.mgi.com (Richard Keeney) writes:

    [lots of good advice on shooting screens, except}

>Use an exposure of at least 2 to 5 seconds to eliminate the horizontal bar
>that can be present if a shorter exposure is used.
>

No.  These exposures are unnecessarily long, and may lead to reciprocity
failure.  In my experience, exposure time should be between 1/2 second and 2
seconds.  1/4 second is OK in an emergency.  Anything shorter than 1/8
second will probably be unsatisfactory.

>
>You will most likely need to increase the exposure 1/2 to 1 stop over the meter
>reading due to reciprocity and stroboscopic effects in the film (typically,
>film is not a perfect linear integrator of light and tends to be underexposed
>when longer exposure times or intermittent exposures like those of the
>flickering light of a CRT are made).  

Not necessary if you follow the advice above...


>When you find a setting that works for your CRT, Lens, and Film combination, be
>sure and write it down as a starting point the next time you have to do this.

Even better: take the time now to design, produce, and save a test image.  I
like something which is predominantly 18% gray, with a few color bars and
somm fine detail.  Put your name in it, and your film has less of a chance
of getting lost.  Iterate until this image generates a dead-center meter
reading for an exposure which provides results you like on "typical" images
that you shoot.  

Then, bracket anyway.  Give your co-author the "1-stop too dark" copies.  

-Ken Sloan