Re: Infrared sensitivity of Silicon PhotoDiodes

["J.Wood" <shopper@xxxxxxxx>]

At 03:21 PM 1/7/98 -0600, you wrote:
>I too had toyed with the idea of an IR meter and became skeptical of the
>market potential - even if the product was just a modification on an
>existing meter (such as when Zone VI modified the Pentax spotmeter).  My
>thought was to add a flip-in/flip-out filter so the ratio of IR intensities
>(in the 700 to 900nm band)  in the scene to visible light could be
>measured. Perhaps a different filter for the Konica folks could be used -
>it gets cumbersome, but by noting the differences between the #87 and 87C
>one gets an idea of how the light is distributed above 650nm.  Most of us
>already have our rules of thumb about bright summer days versus winter
>twilight scenes, but actually measuring the relative proportion of the IR
>would add confidence for me (and would save quite a bit of bracketing and
>therefore money I expect).
>							Elton

You can start with Andrew Davidhazy's proposal, for those using an 87c
filter, to use a piece of a gelatin 87c over the cell on the front of a
Gosssen Luna Pro and using an ISO of 3000. This should work for light
meters with a sliding dome for incident metering. You can find it at
www.rit.edu/"andpph/articles.html. I think it is also on the list's
homepage.  This doesn't cost much at all, in my case it was a piece of
shattered gelatin now replaced by polyester.  I haven't had a chance to try
it out so cannot vouch for it but it looks good.  As does the proposal to
use a piece of [polyester] 87c behind the lens for which I can vouch.
Seems like the same procedure shold work for any filter combination.  

Jim


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End of Infrared-Digest V0 #338
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