Re: IR absor. by H2O

["Rolland Elliott" <rolland_elliott@xxxxxxxxxxx>]

>>>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
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