Re:Tri-Color Exposures using Color IR film

[Gary Beasley <beasleyglb@xxxxxxxxxxxxxx>]

>Date: Mon, 7 Jun 1999 09:59:45 -0700 (PDT)
>From: Rolland Elliott <rolland_elliott@xxxxxxxxx>
>Subject: Tri-Color Exposures using Color IR film
>
>Has anyone ever tried doing a Tri-Color Exposure with
>Kodak's EIR (Color Infrared Film)?
>
>I've seen a few examples of this technique done with
>regular film.  With regular film, a camera is set on a
>tripod and three multiple exposures are made. One
>exposure is with a red filter, the next exposure is
>wtih a blue, and the last exposure is made with a
>green filter. In theory, you are basically breaking up
>white light into the three additive colors, red, blue
>and green, and exposing the film to each color with a
>time delay.
>
>Because of the time delay things that move with in the
>frame become multicolored, typical subjects are moving
>clouds and rushing water.
>
>Unfortunately I'm a little rusty with my color theory,
>so I was wondering if someone on this list could
>validate my approach for doing this with color IR
>film.
>Since color IR film has three light sensitive
>emulsions: one responds to green light, another
>responds to red light , and the final one responds to
>IR light (in addition they all respond to blue light,
>hence the need for a Yellow #12 filter, also known as
>a minus blue filter), I propose the following:
>1. Compose your subject and mount the camera on a
>tripod.
>2.  To obtain correct exposure triple your ISO film
>speed. Example an ISO of 250 would be an 250x3=
>750 ISO.
>2. Set your camera to make three multiple exposures:
>A.  First exposure is with a Yellow #12, Red #25, & IR
>blocking filter.
>B.  Second exposure is with a Yellow #12, Green #58, &
>IR blocking filter.
>C.  Last exposure is with a 87 IR transmission Filter.
>A Yellow #12 filter is not necessary because the 87 IR
>blocks all visible light.
>
>I actually have all of the above filters, so I'm
>thinking of trying this technique in the next few
>weeks, as soon as I see some cool cloud formations. 
>I'd appreciate any feedback on my proposed technique.
>
>One thing I'll deffinitely do is bracket.  Getting the
>correct exposure on one frame of EIR is hard enough,
>with three different exposures, it will be pure hell. 
>I'm also thinking that I'll use a 87C filter for the
>last exposure since I don't think my IR blocking
>filter from B+W blocks out all IR light very
>effectively. This might help to keep the vegetation
>and other highly reflective IR subjects from getting
>over exposed.
>
>Sincerely Rolland Elliott
>P.S. If the false colors of Color IR film are not
>wierd enough for you, this technique should spice up
>your shots.

I've been experimenting with Tri Color effects on color print film and have
found that you have to take the filter factor into account so dividing the
EI rating by thirds is a faulty concept. With the set I use for normal
color (61 green, 25 red, 38a blue) you would shoot each at the normal EI
rating or maybe less for better saturation (slides go the other way ya
know). I dont think you will need the yellow stacked on the set, the other
filters will kill the blue as well. So bracket wide first time around just
to find the ball park. Once in it you may need to adjust for each color
individually.
I want to see what you get!
Gary Beasley
http://beasleyglb.home.mindspring.com/

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