Re: 87 filter with Konica??

[Andrew Davidhazy <ANDPPH@xxxxxxxxxxxxxxxxxx>]

Holly,

I took a look at the instructions that come with the film and it states that
the film's spectral response peak is at 750nm and residual response extends out
to 820nm.

Then I took a look at the spectral transmission of the Wratten 87 filter and
it starts to allow IR to pass at 740nm and reaches maximum transmission at
830nm or so.

The consequence of this combination is that it results in allowing very little
"interaction" between the response of the film and the transmission of the
filter. Note that the recommended exposure combination suggested for use under
bright sun outdoors are f/5.6 @ 1/60 second ... and this is only through a deep
red filter. 

The bottom line is that you probably need to use extreme compensation in terms
of adjusting for using the 87 filter over the lens as opposed to using no filter
or even a #25 filter.

I noticed that Konica does not mention anywhere that the film can be used with
a Wratten 87 filter. This, of course, does not mean it can not be used but I
suspect that the reason they don't suggest it is that the compensation that
needs to be made under average conditions leads to impractical (this is a
subjective determination!) combinations of aperture and exposure time for most
photography situations.

Summary: in your case I would say that your film was underexposed.

imo anyways,

Andy  o o  0 0 o . o  Davidhazy, Imaging and Photo Tech
       \/\/\/\/\/\/          http://www.rit.edu/~andpph
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