Re: IR absor. by H2O

[Stan McQueen <stan@xxxxxxxxxxx>]

At 10:38 PM 03/21/2000 -0500, you wrote:

>>>>This test is a tad too simple. First IR is not completely absorbed by 
>>>>H2O in the first micron of water. However, the light attenuation 
>>>>coefficient is higher than blue light - I do not have the number for 
>>>>wavelengths > 700 nm in front of me - but for 700nm it is about 0.6; 
>>>>for 500nm it is about 0.05 (Fig. 2.18 from Mertens 1970 In-Water 
>>>>Photography, Wiley).
>So to do a more realistic test you probably want a much larger glass. Also 
>it should be flat-sided to avoid confounding optical effects. Say a 1 x 1 
>x 1 meter square glass full of water!>>>
>
>Actually if you want to be realistic, You'd realize that on a practical 
>level IR underwater photography is non exsistant, so why even perform such 
>a test. Based on my informal IR camcorder recordings and viewings, 1 meter 
>of water WOULD NOT absorb IR light to a significant extent.  Heck, I'd 
>even wager that 2 meters of water wouldn't cause that big of a deal. And 
>if you're shooting beyond 2 meters you'll need powerful underwater strobes 
>anyway. Next time I go to the aquarium I'll take along my IR camcorder and 
>some IR film. It amazes me how much speculation there is on this list; 
>less theory & speculation and more practice & experience is my motto.
>
>Peace Rolland


Perhaps you should ask yourself why "on a practical level IR underwater 
photography is non existent". Maybe it's because there is very little IR 
after you descend any significant distance.

Stan

=======================================
IR and other photos by Stan McQueen at http://www.smcqueen.com

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