Re: snow

[Andrew Davidhazy <ANDPPH@xxxxxxxxxxxxxxxxxx>]

> can someone tell me what happens if I shoot the snow with an EIR film? I
> mean: the white of the snow remains white or not?
> Thanks for any help

Claudio,

Hmmmm ... interesting question. I guess it would depend on whether the snow
reflects any incident infrared or not. I mean we would need to know the
spectral reflectance of the snow and the spectral quality of the illumination
that falls on it. Then we would be able to determine the spectral quality of
the radiation reflected towards the camera lens. 

Let us assume that snow reflects zero infrared. Then it is assumed that it
reflects equal amounts of red, gree, and blue since we see it as white. Now in
the film all three layers are sensitive to blue, but this is filtered out by
the yellow filter that you normally would place over the camera lens ... the
#12 is it?. 

Now the top layer is sensitive to blue and infrared and forms cyan dye where
unexposed. The next layer is blue and green sensitive and forms yellow dye
where unexposed ... so this layer essentially gets way overexposed and being a
reversal emulsion it produces no dye. The third layer is blue and red sensitive
and since there is lots of red light, that layer, which forms magenta dye, also
will have no dye in it because the red in the white overexposed the layer.

So, the top layer, being unexposed due to lack of IR reflected from the white
snow, will contain lots of cyan dye while the other two layers will contain no
dye and so the white snow will look cyan.

The actual color will vary and will ultimately dependon the relative amounts of
R, G, IR exposures. Cyan-ish is probably right but I may be all wet on this ...
                                      
cheerio,

Andy  o o  0 0 o . o  Andrew Davidhazy, Imaging and Photo Tech
       \/\/\/\/\/\/   http://www.rit.edu/~andpph  716-475-2592  
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