[LargeFormat] Infrared Filters

[Guy Glorieux]

Diane,
You may just want to check this article by Andrew Davidhazy from RIT in
Rochester.
http://www.rit.edu/~andpph/text-infrared-filter.html

He has done spectral analysis indicating that "the spectral transmission
characteristics of one and two thicknesses of unexposed but developed E6
films and found them to be comparable to that of a Wratten 87 IR
filter".

This means that for the price of a box of 10 4x5 chrome plus
development, you can get 10 4x5 IR filters...

I don't do IR but my wife does and I seem to recal that several years
ago, after reading this article, she tried it on her flash and got very
good results.  She did not try it through the lens, though.

Best,

Guy

P.S.  If you go to the parent directory of that article, at
http://www.rit.edu/~andpph/articles.html
you'll find a number of articles on IR, including digital IR!
In one of the articles, he indicates the following method to get fairly
exact IR exposure data from your light meter in unusual lighting
conditions:

"You may be able to increase your chances of achieving a properly
exposed negative under unusual lighting conditions by covering your
meter's cell with the same filter material which you use over your
camera and calibrating the combination so you consistently end up with
usable images. As a starting point, with a Luna Pro for instance, try a
meter setting of ISO 2400 with the cell covered by an 87C filter.
Under these conditions my meter reads a #14 or so in broad daylight.
Bracket around the exposure recommended by the modified meter and adjust
your ASA rating vs. the 2400 figure to arrive at the speed setting which
gives negatives to your liking. This seems to happen for me when the
meter is set for ISO 2400 but different meters may react differently.
I use the meter only in the "reflected" mode since what is usually
desired is a negative with printable densities rather than one which
properly translates the subject's invisible infrared tonal values".


There is a lot of other fun stuff on that parent directory , such as an
article on how to use your last cup of coffee to process your prints (I
tried that one and it does work...).



----- Original Message -----
From: "Clive Warren" <Clive.Warren@megacycle.co.uk>
To: <largeformat@f32.net>
Sent: Thursday, June 06, 2002 8:37 AM
Subject: [LargeFormat] Infrared Filters


> At 05:17 06/06/02 -0700, Diane Maher wrote:
> Clive,
> Did you ever get the CoCam 87 and 87c filter thing sorted out? I
currently
> have an 87 filter gel, but when I put it into the cokin holder, it
doesn't
> cover the hole completely and in the metal holder for that size that I
> have, it doesn't even fit the P sized holder.  I would love to have a
resin
> P sized 87 and 87c filter.
> Diane
>
> Diane,
>
> The short answer is no!  I have approached several potential
manufacturers
> and either the price or the required quality control didn't work out.
>
> It may interest you to know that someone on the IR list has tested one
of
> the CoCam 89B resin Infrared Filters with a spectrophotometer and it
was on
> the button throughout the curve for the Wratten specifications. To
achieve
> that sort of quality for 87 and 87C filters is expensive.
>
> So you are going to have to use your gels for a while yet. The CoCam
89B
> will work well for MACO Infrared film and that's the only 4x5 Infrared
film
> readily available at the moment.
>
> Cheers,
>             Clive
>
>
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