Refilter factors

[Gary Beasley <beasleyglb@xxxxxxxxxxxxxx>]

>Date: Sun, 5 Sep 1999 03:09:16 +0800
>From: danzig@xxxxxxxxxxxxxx
>Subject: filter factors
>
>I just for the fun of it, decided to try out seeing what the filter 
>factors were on my filters. 
>
>I used a Minolta lightmeter (4F) & I used the lighthing from the one 
>tungsten light I had in the room, and placed the filter over the 
>Luminance ball of the lightmeter.
>
>The readings I got indicated that
>
>Hoya's red filter R25A had a loss of 1 1/3 stops
>
>Hoya Infrared R27 had a loss of 2 stops.
>
>
>
>Is this consistent with everybody else's measurements ?
>
>
>Yours,
>ket
>
Now do the same thing with daylight at high noon. You will find a
difference between some of them. The filter factors on the IR filters
really depend on the amount of IR to visible light. Tungsten having a much
higher ratio of IR  to visible than daylight, you will get different
readings,and the meter does read IR at a lowered sensitivity.
Gary Beasley
http://beasleyglb.home.mindspring.com/

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