Xref: utzoo rec.photo:1969 sci.electronics:2148
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From: korfhage@CS.UCLA.EDU
Newsgroups: rec.photo,sci.electronics
Subject: Re: Homebuilt transmission densitometer?
Message-ID: <11237@shemp.UCLA.EDU>
Date: 9 Feb 88 21:09:53 GMT
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Reply-To: korfhage@CS.UCLA.EDU (Willard Korfhage)
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Organization: UCLA Computer Science Department
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Recently I was wondering about using my color meter as a transmission
densitomiter. I have the low end Beseler model, and it uses a photomultiplier,
seems quite sensitive and has a very small metering aperature.
The general idea, it seems to me, is to compare the unknown density with
some known references until you find a match, or until you get close enough
that you can make a good estimate. The question is how do you get your
reference? A calibrated Kodak step wedge runs about $81 at the local store,
and I didn't care to spend this much money on a whim. An uncalibrated wedge is
less (about $45, as I recall), but then you need to find a densitomiter you
can use to calibrate it. Even cheaper would be to make a series of negatives
of slightly varying exposure and calibrate those. You do have to check for
uneven density in the negatives, but you really need to calibrate only a
very small spot on the negative.

If anybody sees anything wrong with this scheme, I would like to know.
It would not be as accurate as a real densitomiter, but it would seem like
an inexpensive way to figure out 0.1 above film base + fog, or whatever,
with accuracy good enough for a hobbyist. And it would not require finding
a place to put another machine.

   Willard Korfhage

   ARPA : korfhage@cs.ucla.edu
   UUCP : {ucbvax,ihnp4,randvax,trwrb!trwspp,ism780}!ucla-cs!korfhage