Bears and Butterflies

[Andy Finney <andy@xxxxxxxxxxxxxxxx>]

Nice to have a discussion on the group that didn't involve chemistry :-) As
I don't develop my own stuff I was finding the discussion a little too long
and tedious (my problem I know) but the heat question really woke things up
for me at a time when  the low traffic made me think everyone was asleep or
out shooting.  Physics rules OK!

Regarding Polar Bears.  Am I right in thinking that polar bear fur does not
contain any pigment and that the 'colour' is due to refraction/diffraction
effects?  There is the old question of why polar bears are white when they
don't have any predators (except us and I don't think we count) and for
heat absorption they 'ought' to be black.  Is their fur 'black' as far as
IR/ heat (whatever) is concerned or am I barking up the wrong iceberg?

I also read somewhere that butterfly wings are coloured because of
diffraction effects, rather than  pigment.  I would expect that their wings
would therefore give unpredictable results as far as colour IR was
concerned, rather than a straight colour shift.  Has anybody tried this?
Laser-etched surfaces would also give unpredictable results.

Thanks to Bob for his kind comments about the fish-eye tree.  FYI, the
adapter I had (I lent it to someone in the Netherlands and haven't
retrieved it yet) was a Jessops.

Andy



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Topic No. 4