TAKO. INTERNET SEIT 1996.
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[OM] Ultraviolet and polarizers

Subject: [OM] Ultraviolet and polarizers
From: nfoltz <nfoltz@xxxxxxxxxxxxxx>
Date: Wed, 25 Aug 1999 21:54:06 -0700
Artur, Joel,

I've been experimenting with Ultraviolet photography and polarizers a
little
and I've read that ultraviolet light is stongly polarized by polarizer
filters.  A Norwegian
botanist / photographer exploits this to make some beautiful images on
Fuji RTP 64 film which is one of the few films that is particularly
sensitive to ultraviolet light.
    See    http://www.foto.no/nikon/index2.html
If you are using black and white film or  Kodak EIR color infrared film
both of which are quite sensitive to ultraviolet you can use a Wratten
Yellow #12 filter to completely absorb ultraviolet.  The Wratten 85
filter that is used to convert Tungsten balanced film for Daylight use
also completely blocks  Ultraviolet.  Just to check I put a piece of
fluorescent plastic on one side of a some filters and  an ultraviolet
("black light") on the other.  The "black light" puts out long wave
Ultraviolet 360 nanometers or the so called UV-A predominately.
At high altitude or at lower latitudes there will  be more short high
energy wavelengths  like the so-called UV-B and UV-C as well.

But just for fun I did the "Black light" test as follows:
The fluorescent material glowed beneath the following filters that I
tried:
    Polarizer - glowed brightly -- little or no UV attenuation
    UV (0) (Hoya) - glowed almost as brightly -- slight UV attenuation
    Yellow #12 Wratten - no glow -- complete attenuation
    Wratten 85 CC filter - no glow -- complete attenuation
    Blue 82C Wratten - some glow -- some UV attenuation

Multicoated lenses seem to attenuate Ultraviolet light as well which is
one reason
why I like to use my single coated Zuiko 55mm f1.2 on a 7 mm extension
for ultraviolet
macro shots.

So if you are going to go to really high altitude then don't depend on
your polarizer
to block Ultraviolet use it instead to control polarized ultraviolet and
visible wavelenghts.
Watchout for vignetting if you stack filters -- I recommend using a UV
filter unless you
want UV effects.

-- Hank Hogan
    http://www.netcom.com/~flzhgn/uv.htm



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