Re: Infrared sensitivity of Silicon PhotoDiodes

[Gary Beasley <beasleyglb@xxxxxxxxxxxxxx>]

At 09:05 AM 1/7/98 -0800, you wrote:
>
>>
>>This thread reminds me of a discussion I had some months ago about  the
>>possibility of manufacturing an IR exposure meter. I was talking to a
>>small electronics manufacturing concern that makes test equipment for
>>the photographic industry.  They indicated that it would be easy to do
>>but were not sure anyone would be interested.  Is anyone?  I have always
>>had pretty good luck metering (or guessing) IR exposure but it does seem
>>as though an IR meter would makes life easier. And exposure does seem to
>>be the most asked question from thosew just getting into IR work.  What
>>do you all think?
>>
>>Happy New Year!
>>
>>Howard Wells
>
>
>Maybe I am showing my ignorance, but I am not sure what value an IR meter
>would have. If it only measured IR light then what about the visible light
>that many of us that use ir film either unfiltered or with red #25 filters
>which do not cut off all the visible light.  It may be of some help to
>those who use the opaque filters that cut off all the light.
>
>The most valuable meter would be on that had a way to put the filter you
>prefer on the meter.  A meter that had diodes that replicated the spectural
>response of HIE exactly....then what about Konica...or Ilford?
>
>Bill Agee

Good point, Bill. I think the best route would be to find filtration for a
select few IR sensitive meters that would approximate the sensitivity of
the IR film being used. Best place to start, aside from the pure IR 87 and
87C is various red filters to match the films response through the red
filter actually used on the lens. Anything close will probably do, as most
light meters do not precisely match the spectral response of the various
films.
My Minolta III has an attachment that replaces the diffusion dome, used for
reflectance metering. Its very easy to tape a chip of gelatin filter over
the hole to modify its response. Other meters are probably as easy to deal
with. I would have to wonder about the sight through spot meters though.
Gary Beasley
beasleyglb@xxxxxxxxxxxxxx
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End of Infrared-Digest V0 #337
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