RE: Wood effect

[Jesko-Henning Tanke <jesko-henning@xxxxxxxxxxx>]

>> -----Original Message-----
>> the Wood-effect was first reported in 1910 by a guy named Wood when
>> shooting with a filter of 720nm. The effect is caused by the structure of
>> the chlorophyll containing leafs, which absorb most radiation below
>> infrared. Only green gets (mostly) emitted after beeing reflected in the
>> parenchym layer of the leaf. Wavelengths above 680nm are reflected there
>> with no absorbtion at all thus producing the nice light spots on the IR
>> film.
>
>Nope, chlorophyll has nothing to do with it, with the exception that it
>allows infrared radiation to pass right through.  What happens is that
>radiation gets bounced around within the spaces between the cells, and is
>reflected back.  This is the same sort of thing that happens in newly fallen
>snow.  It appears whiter because of the spaces between the flakes, which
>allow light to bounce around and be reflected back more strongly than when
>the flakes are close to one another.
>
>george
>
For the reflection of the infrared the chlorophyll does not play a roll
because the IR radiation passes it anyway, back and forth. BTW, there is
now way for the trees but letting the warm IR rays pass through; otherwise
their leafs would heat up too much thus violating the biochem reaction in
the chlorophyll layer.

What makes the chlorophyll a point of interest for foto application is the
fact that for the human eye the leafs appear darker (absorbtion...) than
for IR sensors. This looks strange and fluffy and thats basically all:
simply a new perspective for the human eye.

I donīt know at which stage of decay during fall the parenchym layer gets
harmed and the leaf stops "reflecting" as described above. But it happens
*after* the chlorophyll was deactivated to allow the tree retracting
valuable minerals. When you shoot dryed hay with IR and Pan material you
will see no difference while living grass appears like leafs (what it is).
(I checked the bio details with a forester...)


Have a nice time
Jesko
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