Xref: utzoo rec.photo:1936 sci.electronics:2098
Path: utzoo!utgpu!water!watmath!clyde!rutgers!ames!sgi!donl
From: donl@foist
Newsgroups: rec.photo,sci.electronics
Subject: Re: Homebuilt transmission densitometer?
Summary: standards for homebuilt densitometers
Message-ID: <10862@sgi.SGI.COM>
Date: 11 Feb 88 23:31:35 GMT
References: <663@houxs.UUCP>
Sender: daemon@sgi.SGI.COM
Distribution: na
Organization: Silicon Graphics Inc, Mountain View, CA
Lines: 31

In article <663@houxs.UUCP>, beyer@houxs.UUCP (J.BEYER) writes:
> R
> eferences: <2659@dcatla.UUCP>
> 
> 
> There is an ANSI standard on transmission densitometry that you should
> look up. While you could make a densitometer in ignorance of the standard,
> and while you could calibrate it to serve your personal needs, your
> numbers will not agree with anyone elses unless your machine conforms
> fairly closely to the standard.

I disagree.  I think that it's fairly easy to calibrate against full-stop
increases and decreases, and that if these are right and you can show that
the meter is pretty linear, you should be pretty gosh-darn close to any
body else's numbers.

> The light color is fairly important as is the sensitivity curve of the
> detector. Of greater importance is the angle of acceptance of the
> detector and the angle of illumination of the source. If you don't
> get these right, you will not be measuring diffuse density, but something
> else. THis will confuse you and everyone else.

Sounds like you're talking about reflection densitometers, which would
definitely be more difficult.  The angle of illumination for transmission
is pretty easy to arrive at -- straight through.  And i haven't even read
the ANSI standard!

- donl

{sun,pyramid,adobe,decwrl,ucbvax,allegra,research}!sgi!donl
donl@sgi.com