Xref: utzoo rec.photo:2003 sci.electronics:2235
Path: utzoo!mnetor!uunet!husc6!hao!ames!sgi!donl
From: donl@foist
Newsgroups: rec.photo,sci.electronics
Subject: Re: Homebuilt transmission densitometer?
Message-ID: <10997@sgi.SGI.COM>
Date: 16 Feb 88 22:08:56 GMT
References: <2659@dcatla.UUCP> <191@ritcv.UUCP>
Sender: daemon@sgi.SGI.COM
Distribution: na
Organization: Silicon Graphics Inc, Mountain View, CA
Lines: 23
Summary: non-standard readouts of density

In article <191@ritcv.UUCP>, kar@ritcv.UUCP (Kenneth A. Reek) writes:
> In article <2659@dcatla.UUCP> ittfb@dcatla.UUCP (Thomas F. Blakely) writes:
> >A handy tool around the Black & White darkroom these days is a
> >transmission densitometer.  While relatively inexpensive ones are
> >available (ca. $200) it might be an interesting project to build
> >one.  Has anyone had any experience along these lines?  
> 
> 	I have built one of these using a CDS cell from Radio Shack.  As was
> pointed out, the spectral sensitivity of the cell (and the lamp, too, for
> that matter) is of little interest to B&W workers.  The problem is to get
> the answer in the right kind of numbers.

I like this because it's cheap and it works!  A handy programmable calculator
or equivalent might be an easier way to get from the wrong numbers to the
right numbers.  If the response of the cell is linear, you should be able to
come up with an equation to turn it into proper density values.  I set up
mine using the first value as zero; it gets subtracted from all the rest as
film base + fog.

- donl

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