Re: IR & Water: a robust debate continues...

[Rolland Elliott <liquidriver@xxxxxxxxx>]

>>90% Transparency for 1 cm = 10% attenuation per cm

The curve is not flat lined from 600 to 900nm it
gradually slopes downward from approximately 100% at
500 nm to about 90% at 900nm.  Therefore all those
math calculations should be taken with a little grain
of salt. When I get time I will scan the graph and
post it on the web.

>>>If you go back over the posts, you were the one who
said that there was NO absorption [of near ir in
water]

You are right. What I meant was that there was little
absorption of near IR in small amounts of water. NO
and NEVER are rather powerful words, that I should not
have used.

>That is assuming you can comprehend and internalize
the data.  
>Something I am beginning to doubt, given your almost
complete reliance solely on 
>direct empirical evidence or books of photographic
imagery...

No need for personal insults.  I tend to like
empiracle data better than theoretical data. 
Frictionless surfaces are hard to come by and the end
result is my goal.  In my opinion theorists tend to be
pessimist. Saying things like: You can’t use AF lenses
for IR photography, you can’t cut down 70mm IR film
into 220 rolls, You can’t take UV pictures unless you
have an expensive quartz lens. Despite what theory
says, all of the above are possible to a certain
extent. 

>If water attenuates Near IR by 10% each centimeter,
how many centimeters of water does the light need to
pass through until 50% of  the near IR is
attenuated..?.......Approximately 6.2 cm,

See my comment above on the gradual sloping of the
graph down to 90% at 900nm.  All I can say is that if
you take a picture with IR film through a 6.2 cm
thickness of water I highly doubt you will have to
compensate by a whole f-stop.  Only way to know for
sure is to try it, but I haven’t done that. I filled
my JOBO print drum full of about 0.6 meters of water
last night and could see the bottom easily using my IR
camcorder with an 88A filter. Yes, it was slightly
darker compared to visual light, but not very
significantly so.

>Besides, this whole argument has provided some very
useful data I never had the time or reason to search
out..

Agreeded.

Peace Rolland 


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