Re: InfraRed and Water - A comprehensive approach - Final Chapter

[Otto Giesenfeld <otto.giesenfeld@xxxxxxxxxxxx>]

--On den 24 mars 2000, 00:45 +0000 Rolland Elliott
<rolland_elliott@xxxxxxxxxxx> wrote:

> to an  appreciable degree."  It also has a graph on page 168 that shows a
> greater  than 90% transmission of IR light below 900nm (which is similar
> to what  Kodak HIE film can record) through 1 cm of water. I'll also dig
> through all  my old negatives and pictures and purge any of them that
> show water that  looks even slightly transparent.

At a transmission of 90% for one centimeter, a foot of water would transmit
only 4%, or decrease the intensity by nearly five f-stops. Density quickly
adds up (or, more to the point, multiplies), since it has to be computed by
an exponential function of the distance.

If you really have photos on IR-sensitive film that show detail of the
bottoms of half-foot-deep ponds, they were probably recorded using a filter
letting through significant amounts of visible light. On the other hand,
some water spilled on top of a table will obviously look almost as
transparent on IR film as in conventional photographs.

Otto Giesenfeld

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