Re: Infrared & Water

[Stan McQueen <stan@xxxxxxxxxxx>]

You keep making my points for me.

At 09:31 AM 03/22/2000 -0800, you wrote:
>Obviously, you have done little or no underwater
>photography. If you "descend any significant distance"
>underwater photographers almost have to use strobes
>99% of the time, which emit plentiful amounts of IR
>and visible light. These strobes make up for the fact
>that there is little IR and visible light at large
>depths.

Because the water absorbs and scatters the long wavelength light.

>Your conslusion is not scientifically sound. Water
>does absorb IR light to a small extent, but not enough
>to make Underwater IR photography impractical.
>Especially considering that many underwater photos are
>taken within one to two meters of the subject and with
>high powered strobes. Try doing it before you say it's
>probably not possible. Peace Rolland

I can take visible light pictures through an 87B filter if I use a powerful 
enough strobe. Does that demonstrate that 87B filters don't absorb visible 
light?

Just because water absorbs and scatters IR does not mean that you can't 
take IR pictures. It means that you won't be able to take them with 
available light unless you are very near the surface. That's why people use 
strobes--not because water doesn't absorb and scatter IR and visible light, 
but because it does. If it didn't they wouldn't need to use strobes. This 
seems so obvious it is hardly worth stating.

Fact: Water absorbs and scatters long wavelength light preferentially 
(i.e., all wavelengths are not affected equally). The deeper you go, the 
bluer it gets. If you can cite any "scientific" study that refutes this, 
then please do so. Your test with a camcorder and a glass of water is 
nowhere near sensitive enough to demonstrate that water does not absorb 
infrared as another poster has said.

Stan


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