Re: no filter with tungsten

[Jim Henderson <hendersonj@xxxxxxxxxxxxxxx>]

The question about the use of continuous, tungsten (3200K or less) light
sources without the red filter is very appropriate.  You can, in fact,
obtain a 2x speed increase with Kodak HIE by eliminating the red filter,
and another 2x speed increase by using infrared-rich tungsten light
sources.  The proportion of blue light to which HIE is VERY sensitive is so
low compared with red and infrared wavelengths that I rarely use a filter
when photographing with such light sources.  Concerts are good examples of
scenes which employ hot tungsten lights.  You could rate HIE two stops
faster under these conditions and still obtain the IR effect.  

I once did a "test" using all the wratten filters, starting with the dark
blue #47B and ending with the #25 red.  I found that all the filters
consistently "slowed" the film speed down by one stop when using ANY
filter.  As you use filters which progressively eliminate more and more
blue-yellow-green wavelengths you can observe a change in:  sky, water
surface reflections, foliage, and skin tone rendition.  (Laurie White's
Infrared manual has a pretty good example of photographs of the same
subject used with different filters.  The book is really quite strong with
its use of visual examples of  infrared photography.)

Jim Henderson
Applied Scientific Photography

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