Re: Exposure and development control

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 24 Oct 96 at 12:58, TAMMY L. SULLIVAN wrote:

> Willem,
> 
> Glad you've read the book ... I'm still thumbing thru it.  Weird how they took
> photographs with IR of the oddest things.  Yuk.
> 
> Tammy

A truely magic detail, page 259-260:

"The explanation of the white appearance will be clear from a
consideration of Figure 55, which is taken from the work of
Willstaetter and Stoll, and which shows how light is reflected
internally in a leaf. The light passes through the epidermis and the
palisade cells, but is scattered diffusely and even reflected back
towards its source in the spongy parenchyma, the interstices between
which are filled with air. Mecke and Baldwin pointed out he
similarity of behaviour between the leaf and freshly fallen snow
(!!!), the bright reflection of which is due to the presence of air
between the small ice crystals. If snow is pressed or tamped, it
becomes darker and transparent. The same occurs in case of a leaf.
If the air is removed by the leaf being placed in a vacuum, and if
it then placed in water to fill the air spaces, no difference
results which is visible to the eye, since the chlorophyll absorbs
most of the light. In the infrared, however, to which chlorophyll is
transparent, the bright reflection of the leaf is almost completely
lost, and the leaf becoms relatively transparent."


There you have it. The reflection of snow and foliage are based on 
exactly the same principle!

Flabbergasting....8-)) 
--
Bye,

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      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]

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Topic No. 6