Re: E-6 Infrared Filter?

[Andrew Davidhazy <ANDPPH@xxxxxxxxxxxxxxxxxx>]

Mark,

It is true. It works. But it is not as good a solution as using "real" filters.
You have to realize it is an improvisation. But, at least it will demonstrate
to the students that things they can hardly if at all see through (especially
two layers) IR film can readily see IR through. You will get the familiar white
trees effect and dark skies, etc.

Because the film is somewhat turbid the images may not be tack sharp ... but
that means the images actually have a charm of their own. When used over a
flash this is of course not a problem. However, you shouyld be careful not to
blast a flashead repeatedly into a IR filter covering the reflector because you
could build up unusual levels of heat. On the other hand this is also a problem
with "regular" IR filters blocking a flashead too albeit maybe not as severe.

I did the testing for this and published absorption curves some years back and
you can probably find the reference to it ... wait, i'll get it:

from the PhotoForum's (my!) FAQ files  ... section 19:

     ftp://vmsftp.rit.edu/pub/ritphoto/photoforum/faq-19

--------------------------------------------------------------------------------
Note 19.01   -< Making an Improvised Infrared Transmitting Filter >-
--------------------------------------------------------------------------------
                     Visually Opaque, Infrared Transparent
 
I just determined what I had long suspected. I measured the spectral
transmission characteristics of one and two thicknesses of unexposed but
developed E6 films and found them to be comparable to that of a Wratten 87 IR 
filter. In addition I also made some pix on HIE film through two sheets of 
Dmax EF sheet film and compared the pix to some taken through a "standard" IR
filter, the Wratten 87. 
 
The result of this is that it appears that one thickness of E6 film is roughly
the equivalent of an 87 filter but with a broader spectral response and with
some 1% transmission valleys at 500 and 600 nm. Its transmission starts to drop
from 1% at 700 nm to about 95% at 800 nm. Two thicknesses of D max E6 are 
basically visually opaque with transmission dropping rapidly starting at 720 nm
and dropping quite rapidly to 90% or so at 850 nm.
 
Maybe they might be closer to what a 88 is. Basically the 2 sheets of E6 simply
do not have as steep of a cutoff as the Wratten filters do nor as good a
maximum transmittance. But they are serviceable!!! especially for placing over
a flashgun where expensive Wratten filters tend to fry and buckle!
 
Picture-taking wise, the two thicknesses of E6 film did not seem to degrade
image sharpness significantly when used with 4x5 format. I have not tested
35mm. They would obviously not matter much when used over a flash for
inconspicuous flash photography at parties, etc.! (camera lens with or without
additional  filter over it).
 
If you would like a copy of the spectral transmission curves for the 1 and 2 
sheets of E6 film, and that of an 87 filter, just send me some e-mail along 
with your RIT postal address. If you do not hear from me in a few weeks (!) 
jog my memory.
 
Andy
    
.... any E-6 film will work ... even Kodachrome (which is not E-6!)


>   Is it true that a person can use an Unexposed but Developed sheet of E-6
> film for an infrared filter?  Are the results good?  Will it work on a flash?
>  Does it matter what brand or type of film is used?   Does anyone have
> examples scanned in using this process?
>   Sorry for all of the questions, but I'm trying to find a cheaper way for my
> students to use an infrared filter.

> Thanks,

> Mark "Zman"
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