Re: Previsualizing IR

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On  8 Nov 00 at 16:00, ADavidhazy wrote:

> Previsualizing generally means being able to predict what a scene is going to
> look like on a final print. This is rather difficult to do (in my opinion)
> since we can not perceive infrared in the same manner that infrared sensitive
> film used with red or infrared transmitting filters does. So, at best, we have
> a "gut" feeling of what something might look like ... or a wish for something
> magical to happen.
> 
> On the other hand, as has been discussed on this list several times, there are
> tools available that DO allow a _certain_ amount of previsualization to take
> place. Use of a IR sensitive camcorder such as the Sony ones with "night shot"
> capability is one way to go. Another is the use of an infrared image converter 
> device such as often used in darkroom conditions ... sniperscopes and similar
> devices many now exported from Russia and sold by outfits like Sharper Image
> and Edmund Scientific.

One item/concept/method not mentioned here (nor in any literature
that I know of) is the use of a 'borderline' dark-red/IR filter....on
the edge of visible and opaque....technically inbetween #89B
(reasonable visibility, only a very faint hint of IR (light
foliage)) and #88A (nearly opaque, only contours can be seen in
strong light).
Within the Kodak Wratten system, this inbetween color is #88, 
according to an old 1938 catalog....interesting detail: in that 
catalog, #88 is decribed as 'as used by J.W. Wood' ....

It requires that you shade your eye from backlight, when looking 
through the filter....but that is a little price to pay for being 
able to see really large contrasts between soil and 
foliage/grass....remember, the Wood-effect starts at 695nm, well 
below the visible limit (of 780nm)....it's only a matter of matching 
the transmission curve of the filter to the curve of the human 
eye....and from the experiments/samples I have done/seen, there's not 
much margin to get it right, probably within 10nm accuracy....below that, the 
visible spectrum prevails, and the Wood-effect dissapears 
(relatively, overexposed by the visible spectrum), above that, it 
gets too dark, and you only see contours (it's possible that longer 
adaption of the eye to darkness could improve this, but that's hardly 
practical as a IR-preview method).

Problem: #88 isn't made by Kodak anymore (most IR-colors aren't
anymore, but this one must have been out of production since a long
time, since #88 isn't listed in any overviews from the last
decades).
(if anyone knows otherwise, please step forward....would also love to 
get my hands on such a Wratten #88, as a reference for the color-samples I 
have collected from other manufacturers over the years (among which 
some production-errors, lighter than intended, but remarkably suited 
for this application....best inventions are done by mistake....:))

I have also been pondering about fabricating a similar
IR-preview-filter as is made/used for black&white previewing (this is a
Wratten #97 I believe), and even color (no idea whether that matches
a Wratten number); both consist of an eye-cup with a filter mounted 
inside....more common in cinematography I believe.

If anyone is interested in such a product, please mail me 
privately....


--                 
Bye,

Willem-Jan Markerink

      The desire to understand 
is sometimes far less intelligent than
     the inability to understand

<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
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