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Re[2]: [OM] Life of a selenium cell (was Trip 35 Info)

Subject: Re[2]: [OM] Life of a selenium cell (was Trip 35 Info)
From: Dave Haynie <dhaynie@xxxxxxxxxx>
Date: Tue, 12 Jan 1999 03:03:13 -0500 (EST)
On Mon, 11 Jan 1999 14:23:04 -0500, John Hermanson <omtech@xxxxxxxxx> jammed 
all night, and by sunrise was overheard remarking:

> The life of a selenium cell is unpredictable but it is one of the
> reasons they are not used in cameras anymore (imho).

I doubt it's an issue. There are plenty of good reasons not to use them.
For one, they're not very sensitive, and typically require a large area
for metering, not a good match with today's small cameras that are
expected to meter well under low light conditions. Such a large surface
are also makes directed metering impossible. 

I think there may be some spectral response issues, but I don't recall
the details (ages ago, I had a hand-held light meter based on a selenium
cell). Unlike CdS ( photoresistors) or silicon photodiodes, the selenium
cells actually produce a voltage in response to light (the others modify
an existing voltage supplied by the camera). 

Only the photodiodes have a fast enough response for OTF metering.
--
Dave Haynie  | V.P. Technology, Met@box Infonet, AG |  http://www.metabox.de
Be Dev #2024 | NB851 Powered! | Amiga 2000, 3000, 4000, PIOS One



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