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Re: [OM] Colour Balance of Slide Film

Subject: Re: [OM] Colour Balance of Slide Film
From: Donald Shedrick <shedridc@xxxxxxxxx>
Date: Mon, 13 Jan 2003 16:56:39 -0800 (PST)
I have been using Kodachrome 25 and 64 for nearly 30 years and have
always been very pleased with the color balance.  I shot a lot of
snow scenes while skiing and used mostly K25, which gave incredible
snow color and detail within the snow.  K64 was very good, but not
quite as good, main difference was K25's greater exposure latitude. 
And all my old Kodachromes - and my Dad's even older ones, are as
good as new stored in their original yellow cardboard boxes.  I tried
K200 only a few times, and did not like it nearly as well as K64. The
K200 was to me a little yellow and lacked saturation. 

As for the pink leader, I can tell you K200 definitely turns pink
when it saturates with bright light.  I found this out when
photographing the total solar eclipse in 1999.  The bright corona,
which is nearly pure white, had a pink ring around it at a certain
saturation point, but not at the highest level of overexposure.  Very
strange action.  I since switched to E200 for eclipses, which does
not do this at all.  I also use E200 when I want less contrast than
Kodachrome.  Under some lighting conditions (like bright sun and
shade in the same shot) I find Kodachrome's high contrast to be a
problem getting the right exposure.

For example of the pink corona with K200:
http://groups.msn.com/firstlightimaging/1999blackseasolareclipse.msnw?action=ShowPhoto&PhotoID=159

For example of a proper looking corona with E200:
http://groups.msn.com/firstlightimaging/2001africantotalsolareclipse.msnw?action=ShowPhoto&PhotoID=51

Cheers,
Don Shedrick

--- CyberSimian <CyberSimian2@xxxxxxxxxxxxxx> wrote:
> I was looking through some slides to select my "Old Age" TOPE
> entry, and I
> was struck once again by something that I first noticed several
> years ago
> (see below).  The slides were shot on Kodachrome 200 film:
> 
> o   I shoot Kodachrome because I want the archival permanence of
> Kodachrome
> (immunity to fading over decades).
> 
> o   I shoot 200ASA speed because 64ASA is too slow to handhold when
> I want
> reasonable depth of field and am using a polariser.
> 
> What I noticed was the colour balance of the film leader.  That is
> the bit
> of film that is completely fogged when loading the film, and so
> should be
> completely transparent (this is slide film!).  Placing the leader
> on a white
> sheet of paper shows that the leader has a slight magenta cast. 
> Numerous
> films have shown this over the years (all Kodachrome), so I don't
> think that
> this is due to improper storage or airport X-ray machines.  Some
> thoughts:
> 
> (1)  The entire film might have a slight magenta cast.  However,
> the human
> eye/brain is notorious for correcting for colour casts and making
> things
> look "normal", so a non-expert might think that the slides are OK
> (they look
> OK to me), whilst an expert might notice the slight colour cast. 
> If most
> people don't notice the colour cast, Kodak might have decided that
> this was
> an acceptable compromise to make when designing the film.  If the
> entire
> film DOES have a colour cast by design, it implies that one could
> use a
> colour-correcting filter permanently on the lens to obtain slides
> with
> neutral colour balance.
> 
> (2)  Most reasonably-knowledgeable photographers are familiar with
> the
> concept of reciprocity failure.  Colour films suffer from
> differential
> reciprocity failure, that is, each colour layer in the emulsion
> fails
> reciprocally at a different rate.  The result is that exposures
> that are
> very long (seconds) or very short (1/10,000 second) acquire colour
> casts.
> One could regard the film leader as a very-long exposure, although
> since the
> film is completely exposed there might be other effects coming into
> play.
> However, it may be that completely exposed film also acquires a
> colour cast.
> If the colour cast affects only long exposures or gross over
> exposure,
> correctly exposed frames might have neutral colour balance, and
> hence NOT
> need a colour-correcting filter.  If this is true, the colour
> balance of the
> film leader cannot be used to deduce anything about the colour
> balance of
> correctly exposed frames.
> 
> So, which do you think is the correct explanation -- (1) or (2) or
> something
> else?
> 
> -- from Cy in the UK
> 
> 
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=====




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