Re: nice spectral plots of both film & filters

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

On 20 Apr 98 at 0:20, Dan Cardish wrote:

> One thing that these charts drives home to me is the relative utility (or
> lack of) of the various 87 series filters.  I have never been able to see
> the reasoning behind using anything other than a #87 filter with HIE film.
>  Since the 87 is visually opaque, it should be the most desirable for
> non-scientific uses. The 'higher' order filters such as the 87C,B,A all cut
> off useful IR from the film.  I can't see how there can be any gain in
> image quality by eliminating any of the IR wavelengths past 700 nm.

A #87 already cuts off usefull IR, at least when considering that the 
Wood-effect starts at 695nm.

Yet most people see a difference between #89B and #87C, and the same
holds for anything darker. And even if the Wood-effect doesn't
increase nor alter, there are still many dead objects that can
change their reflection in the IR spectrum. Another argument is that
scattering of light in the atmosphere goes down with a power 4 
compared to wavelength....the deeper into IR, the better.
Don't look at it as using the film spectrum inefficient, look at it 
as slicing an even more special part of the spectrum, and putting it 
on film. Yes, it is inefficient when looking at exposure times, but 
that is what tripods are for!....:-))

I won't rest until I have a batch of #87B in square resin, and #87A
is on the to-do list as well....;-))

Btw, unlike Kodak, which has skipped most of its darker and lighter
gelatine filters (other than #87/C), I still have a source of
gelatine filters in these color ranges. Not cheap though, US$1 pro
square cm, and relatively vulnerable gelatine (although they seem
less affected by moisture/fingerprints) but at least I have a source
of them (wish I could get all these colors in both thin and thick
polyester foil....;-((




- -- 
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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End of Infrared-Digest V0 #520
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