Re: Wratten 25 vs. Wratten 29

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

On 19 Oct 96 at 6:08, Robert Long wrote:

> Walter Clark, writing about the original Kodak 35mm IR emulsion, says
> that there is no practical difference between these two filters
> because that emulsion is insensitive to the red range in which there
> is a difference between the filters.  

I guess you are referring to his comment on page 22?

> His wedge spectrogram does show
> diminishing sensitivity through the red range before dropping off
> altogether in the yellow-greens.  I've never seen a wedge spectrogram
> for HIE.  Does it behave the same way?

Nope; HIE does not show a real gap, and it also extends further than 
the old emulsion (950nm vw 850nm). 
Somehow the old emulsion resembles Konica 750....
 
> What I'm really asking is, after having gone to considerable trouble
> to find a Wratten 29, does it really do nothing for me that my old
> Wratten 25s don't?

Well, I have had more people asking me about a #29 solution, but I 
have difficulty understanding the need for such a slight improvement 
over #25, considering that both #70 and #89B can most likely also be 
used as a visibly transparant filter. Although possible as a resin 
square, I don't think a #29 will ever end up in my arsenal....



 
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      The desire to understand 
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<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]

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Topic No. 2