Re: Question about Color UV photography & why you can get various colors with UV reflectance photography

[Rolland Elliott <rolland_elliott@xxxxxxxxx>]

Hello Bjorn Rorslett,

Thanks for taking the time to write back to me.  I
have some other questions.  You wrote: "I would like
to add that it's only by employing a dedicated UV lens
that these colours are readily apparent."

I was wondering if you have obtained various colors
(blues, reds, whites, etc) when doing UV pinhole
phtography? Your one UV pinhole picture on your web
page is a monochrome blue color. So, I'm guessing that
it's not possible?  
Also do you know of any other quartz lenses that are
cheaper than the Nikkor 105mm f/4.5 UV lens?  This
lens currently sells for over $3000 US dollars.  
After reading your post it sounds like the only way to
get UV color photos is by using this lens.  By the
way, have you ever tried using Nikkon EL enlarging
lenses on a Nikon camera (with a Nikon bellows unit
for focusing) for UV color photography?  Nikon's
literature states that these enlarging lenses are
corrected in the UV range above 350 nm.

thanks again,  rolland elliott

--- NFOTO Bjorn Rorslett <nikon@xxxxxxx> wrote:
> At 12:19 17.04.99 -0700, you wrote:
> >Hello Bjørn Rørslett,
> >
> >I enjoyed looking through your web site and reading
> >your review of the "F5 light".  I have a question
> >regarding your color UV photographs.
> >
> >Theoretically, your color pictures should be
> >monochromatic.  The pictures should be basically be
> >shades of blue with underexposed black areas and
> >overexposed white areas.  However, your pictures
> also
> >have the color red in them!  How is this possible
> if
> >the Nikkon 18A filter you are using is supposed to
> >block all visible light and therefore all red
> >wavelengths?  The only explanation I can think of
> is
> >that this Nikon 18A filter actually lets some deep
> red
> >wavelengths to pass through to which the film, Fuji
> >RTP, is sensitive to.  Thus your pictures have
> three
> >colors in them, red blue and white.  Is my theory
> >correct?  Thanks for the feedback!
> >
> >Sincerely, Rolland Elliott
> 
> hi
> 
> I for one was amazed by the additional colours when
> I first started doing
> UV colour photography. I believed the UV rendition
> would be all bluish.
> 
> My interpretation of this is as follows,
> 
> The UV bandpass filters are less than perfect so do
> allow a slight amount
> of extra light to pass. Seems this happens in the
> extreme deep red (above
> 690 nm) and extending into the near-IR. This in fact
> is a common feature of
> *all* silver-based UV bandpass filters,  not just
> the Nikon filter. 
> 
> This sidelobe transmits a very low amount of
> incident light so one should
> think it would be to weak to give a photographic
> impression on the film.
> However, one has to take into account the very low
> UV sensitivity of the
> films (after all they do include a UV filter layer)
> compared to their much
> higher red sensitivity.
> 
> Thus, the colours result from the spectral
> reflectance properties of the
> objects being imaged. They can be interpreted the
> following way,
> 
> white: all spectral bands (UV +visible) reflected
> black: all spectral bands absorbed
> blue: high UV reflectance, low red+yellow
> reflectance
> red: negligible UV reflectance, high red+yellow
> reflectance
> 
> Thus, the variable amount of UV light reflected, in
> conjunction with the
> colour-band reflectance of the object, translates
> into a quite wide range
> of colours on the film. In fact, one can have
> yellowish, greenish and
> magenta shades too.
> 
> UV colour photography is all about exploring and
> using this colour palette
> to its full advantage. One simply has to learn how
> the scene is captured in
> UV.
> 
> I would like to add that it's only by employing a
> dedicated UV lens that
> these colours are readily apparent. Ordinary lenses
> transmits so low in UV
> that the deep red/near-IR transmittance of the
> bandpass filter will
> dominate and the ensuing image will have a strong
> reddish cast.
> 
> Hope this information helps. Do not hesitate to
> contact me again if I can
> be of any assistance.
> 
> /bjørn/
> Bjørn Rørslett -NN/Nærfoto
> Professional Nature Photographer, Ph.D.
> Kongsberggt. 13, N-0468 Oslo, Norway
> Phone: +47 22 18 26 61 Fax: +47 22 95 24 80 Mobile:
> +47 90 60 03 90
> e-mail: nikon@xxxxxxx   web:
> http://www.foto.no/nikon
> 

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