Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!mailrus!iuvax!purdue!mentor.cc.purdue.edu!pur-ee!3ksnn64
From: 3ksnn64@pur-ee.UUCP (Joe Cychosz)
Newsgroups: comp.graphics
Subject: Re: photographing screens
Message-ID: <13793@pur-ee.UUCP>
Date: 11 Dec 89 22:11:16 GMT
References: <5204.2581ACEC@urchin.fidonet.org>
Reply-To: 3ksnn64@pur-ee.UUCP (Joe Cychosz)
Organization: Purdue University Engineering Computer Network
Lines: 21

In article <5204.2581ACEC@urchin.fidonet.org> Leo.Waltz@f270.n106.z1.fidonet.org (Leo Waltz) writes:
>I'm also wondering about proper focal length of lenses to use to minimize 
>the corner distortion of some monitors.  I assume that the greater the 
>focal length the better.  Any comments ?

This is in general true.  However when working with Macro-zoom lens such
as the Nikon 70-210mm.  The problem is in the distoraton in the lens system
at 210mm.  For a 70-210mm Macro Nikon I use about 2 ft at 70mm.
This contradicts what one might think
in that one would expect the flattest photo to appear by getting as far
away as possible and shooting with as long of a lens as possible.  The
problem is in the distoration in the lens system at 210mm.  Keep in mind
that a macro lens works on a series of approximations.  What results
is concave pillowing which is oppisite of the convex pillowing caused by
the curvature of the screen.  The optimal flat picture occurs when the
convexed pillowing of the screen is balanced with the concaved pillowing of
the distortion in the lens system.  Since I do not have a straight 200mm
lens, I have not been able to study and measure the distortion in the
macro.

Joe