Re[2]: [LargeFormat] home densitometry

[Les Meehan]

Don

Use an enlarging lens reversed on the front of the meter instead of 
close-up lens, it will do the same thing i.e. focus the image close. I cut 
a small hole (1/2 inch) in black paper to mask unwanted light. It is pretty 
accurate, and 1/3rd stop is 0.1 density step as you said.

Les

-----Original Message-----
From:	Don Wilkes [SMTP:Don.Wilkes@gems9.gov.bc.ca]
Sent:	16 August 2001 18:11
To:	largeformat@f32.net
Cc:	Don Wilkes
Subject:	Re[2]: [LargeFormat] home densitometry

At 10:49 AM 8/16/01 +0200, Frantisek Vlcek wrote:

>Don, I think I have an article on it somewhere, I will have a look in
>my computer (the "archive" is in pretty bad shape now :( .

That'd be fabulous, Frantisek!  Please let me know if you come up with
anything.

> I remember the bit about closeup lenses. He inserted between them a ring
of black
>paper, to eliminate reflections and flare.

Ah -- new information!  That wasn't at all obvious from the illustration.
Do you have any memory of how big a hole he cut in the black paper?

>You don't have to buy Kenkos -

I was pretty sure about that; I was wondering if the #10 happened to be
some designation peculiar to the Kenko brand.  That is, a "Kenko #10" might
be equivalent to a "Pentax #3" or something...


>you can get 46mm filters inexpensively, some used or even busted
>filters will do, just remove the remains of glass, and put the CU lens
>cut to diameter into it, and screw in the retainer.

Now there's a good idea... I did pick up a 46-49 step-up ring pretty
cheaply.  The larger size, being standard for most Pentax lenses, would
make finding close-up filters a bit easier, I thought.  My local
used-photo-toys store had quite a big drawer of assorted 49mm filters, but
I was mildly surprised that they were all about $10, which seemed a tad
high for an old UV filter!


>Please share your experience, I have an Spotmeter V

I certainly shall.  If the weather stays nice and clear after work, I'm
going to shoot a couple of sheets at Zone I, bracketing the E.I. from the
film's nominal speed down to something less than half that.  I'll keep the
dark slide half-way in on at least one sheet, so I'll get a good-sized area
of no exposure too.  My goal is to find the exposure that yields a density
of 1/3 of a stop more than film-base+fog.  That should be about 0.10,
shouldn't it?  With a full or half-sheet to meter on the light table, not
having closup filters shouldn't be a problem.  If I can find some tubing
that'll slip over the meter's lens barrel, I'll be able to keep the
meter-to-film distance constant.  Otherwise, I'll mount the meter on a
tripod, and swap film sheets below it.

If anyone out there spots some flaws in what I'm planning, please let me
know.  It seems to make sense to me, but I'm certainly open to suggestions!


>more expensive here in Europe than in Canada (unless you want to trust
>a 50 year old densitometer big like your computer monitor, propably
>great in its time, but now? calibration? ...)

I saw an old Kodak one for sale here last winter, for about $100, and
seriously thought about it.  But, I didn't have much money to spare at the
time, and I had the same thoughts about what it might cost to get it
calibrated properly -- that is, *IF* it could still be calibrated!  It'd be
great to have, and much easier to use than fiddling about with a spotmeter,
but how often would I really need such an extravagance?  I don't tend to
change film emulsions much (FP 4 is hard to beat), and it's unlikely I'm
going to tinker much with how I process it.  So, once I nail down my base
exposure, I shouldn't need to do much more "home densitometry" --  I'd much
rather be out taking pictures, or making enlargements...


Cheers,
\don

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