Re: Interview with Walter Clark

[Patrick Bollen <patrick.bollen@xxxxxxxxx>]

Willem-Jan Markerink wrote:
> 
> Hi gang,
> 
> Here the promised translation, extracted from the German book
> "Moderne Infrarot und UV-photography", written by Guenter Spitzing,
> printed in 1992. Note that this interview is much older, it also is
> included in his 1978 edition (I have the Dutch translation of that).
> He also wrote a book in 1967, which I hope to find one day....;-))
> 
> xxxxxxx The Infrared Aerial Photograph xxxxxxx
> 
> Walter Clark of Kodak Research Laboratories in Rochester, USA,
> courteously allowed me to interview him on the subject of aerial
> photography. Focus of our conversation was the topical infrared color
> material, which is not only produced as 35mm, but mainly in aerial
> photography formats, under the name Aero Ektachrome Infrared Film.
> 
> Question:
>    Mr. Clark, you have been involved in the development of infrared film
> from the very beginning. At what time did you discover the fact that
> haze can be penetrated with IR-photography?
> 
> Walter Clark:
>    Real IR-photography started in 1931. At that time Kodak
> started with the production of near-IR sensitive materials, with the same
> overall sensitivity as normal films. With self-sensitized (sp?)
> emulsions there were much earlier experiments, in astronomy and
> spectrography. Even in 1907, in the person of Wood, it was known that
> materials sensitive beyond 680nm could penetrate dust and record
> foliage as white.
> 
> Question:
>    Already in 1940, 5 years after the launch of the first color film,
> you consided the development of color-IR film. Why did this material
> look so promising for aerial photography?
> 
> Walter Clark:
>    Modern color photography started in 1935 with the launch of
> Kodachrome. In 1937 we, and more importantly the US Air Force,
> performed aerial photograph experiments. In 1938, Brad Washburn and
> I, Walter Clark, shot many aerial color photos in Alaska on rolls of 9.5"
> aero film. In 1940, US Air Forces demanded Kodachrome films for aerial
> use. At that time, we explained that the processing of these films
> was too complicated for military use. But only one year later, in
> 1941, our experiments with build-in color-couplers performed so well
> that a much easier to process film could be produced. So for the US
> Air Forces, we released the so called Kodachrome-Aero-Reversal-Film.
>    Also in these days we researched the aerial photography on the
> potential of camouflage recognition. We considered the possibility of
> combining IR-characteristics with color contrasts. I believe that the
> first thoughts about a two-color separation camera working according
> the Technicolor principes originates from D.A. Spencer and A.
> Marriage at Kodak in London. This idea was then lifted to Kodak
> Research Laboratories in the US, in the person of Mannes, Jelly,
> Wilder, Copstaff and me. We then considered the use of the multiple
> layer color film, in which one layer should be infrared-sensitive.
> Many combinations were tested, in particular a two-layer/two-color
> system and two three-layer/three-color films.
>    One of these three-layer films was then selected, and released to
> the US Air Forces as Kodacolor Aero-Reversal-Film for camouflage
> recognition. The modern vision of this is the Ektrachrome
> Aero-Infrared-Film.
>    Color-IR is more usefull than black&white-IR, since color contrast
> is easier detected than grey-scale contrast.
> 
> Question:
>    The b&w IR films that are used in aerial photography are sensitive
> for the very near infrared. Do you exlude films between 1000 and
> 1500nm mainly because of stock problems, long exposure times and
> such? Or does this range of IR not bring any additional information?
> 
> Walter Clark:
>    The practical limit is around 1340nm. Films with a sensitivity of
> more than 950nm are to slow for aerial photography. Such materials
> are only recommended for spectroscopy.
> 
> Question:
>    Again a question about the color-IR material! Is this special film
> type always considered better than normal color film?
> 
> Walter Clark:
>    No!, certainly not. The color-IR film should only be considered a
> better solution if strong IR-reflections are present.
> 
> Question:
>    How is this question answered for aerial photography if we compare
> b&w-IR with color-IR?
> 
> Walter Clark:
>    This kind of questions are still being investigated currently. In the
> UK there is an experiment right now, to assess whether the harvest
> time of field fruits is better detected with color- or b&w-IR.
>    As a last remark I would like to comment that - even apart from
> aerial photography - several tests are underway which should tell us
> where color-IR can have advantages over b&w-IR.
> 
> [final alinea from Guenter Spitzing]
> 
>    After these words from the mouth of an expert, I like to add a few
> comments:
>    The Crazy-Color film acts, as mentioned before, very contrasty. This
> is explained with its original application: aerial photography. The
> by haze scattered light between airplane and surface of the earth
> decreases contrast strongly. The circumstances under which most of
> these aerial photo missions take place remind us of copying
> topographic carts by hand, drawing on a diffuse transparant piece of
> paper. The outlines pour through, but the contrast is gone. Like
> within transparent paper, light scatters on dust particles and water
> molecules, drifting around in the air. The higher the plane, the
> stronger this lack of contrast. The haze penetration of IR-rays, but
> also the very contrasty acting color-IR film compensate this loss of
> contrast. Normal Aero-films from Kodak - even ordinary non-IR films -
> also tend to result in large contrasts.
>    Apart from IR-photo's there are currently also thermographic images
> being taken from air planes. For nightly aerial images artificial
> light - for example in the form of 'christmas trees' - is not
> neccessary anymore. Very recently the US Air Force ordered the
> development of a special UV-camera for air reconnaisance at Perkin
> Elmer Corporation. This camera is used together with a set of
> interference filters, which only let pass a small spectral band of
> light. How UV-reflection photography is related to especially aerial
> photography....only Lord and the Air Force knows.
>    UV is possibly involved because UV-sensitive films with enormous
> resolution can be used.
> 
> 
> --
> 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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