(Fwd) IR and UV photography and viewing

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

Some quite interesting notes sent to me in a private mail:

------- Forwarded Message Follows -------
Date:          Thu, 07 Jan 1999 11:25:05 -0500
From:          "A. F. C. St. Clair" <fred.st.clair@xxxxxxxx>
Subject:       IR and UV photography and viewing
To:            w.j.markerink@xxxxx
Reply-to:      nermal@xxxxxxxxxxxx
Organization:  Lockheed/Martin

I read with interest your experiences with a night-vision viewer
equipped with an IR filter (being able to see a bird through the
folage).  

It reminds me of my first attempts to take IR photographs (Kodak IR
film  +87c filter (or the type "A" or "F" filters).  I was given a type
18A filter and I found that it passed enough near IR and UV that I had
reasonable visual acuity after about 5 minutes (in daylight).  The
visual effect upon the folage was the same as photographs taken with the
type "F" (deep red) filter and IR film.  

I found that about 50% of the individuals could also perceive near-IR
light through this filter (18A and a type 87C) but the rest could not.  

A camera loadee with Ektachrome duplicating film with a 18A filter was
recommended for taking photographs of "unusual aerial phenomena" by one
author.  I do not have the title of the book in front of me.  It turned
out that the duplicating film had lower contrast and extended IR and UV
sensitivity that had to be compensated by the use of a filter pack (UV
and IR blocking filter(s) in the light source) to give proper results.

Feel free to contact me at: nermal@xxxxxxxxxxxx

--                 
Bye,

Willem-Jan Markerink


      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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