Archived posting to the Leica Users Group, 2000/12/14

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Subject: Re: [Leica] Leicaflex mk1 light metering question
From: Martin Howard <howard.390@osu.edu>
Date: Thu, 14 Dec 2000 21:42:49 -0500

weber_leou@itri.org.tw jotted down the following:

> Why the CdS meter cell need power?

I believe that all CdS meters need batteries: the CdS cell regulates a
circuit by varying resistance as light falls upon it.  A battery is needed
to drive the circuit and provide the voltage/current to vary, which then
drives the read-out.

Selenium meters generate voltage/current in response to infalling light and
do not require batteries, but function poorly in low light and -- if I
recall correctly -- are prone to "temporary blindness" by exposure to strong
light sources, causing them to give incorrect readings to weaker light until
they've "recovered" for a little while.

More info at:
 
    http://www.picture.com/infocus/articleSelect.asp?MODE=GETSELECTED&ID=26

M.

- -- 
Martin Howard                     |
Visiting Scholar, CSEL, OSU       |    What boots up must come down.
email: howard.390@osu.edu         |
www: http://mvhoward.i.am/        +---------------------------------------

Replies: Reply from "A.H.SCHMIDT" <horsts@primus.com.au> (Re: [Leica] Leicaflex mk1 light metering question)
Reply from john <bosjohn@mediaone.net> (Re: [Leica] Leicaflex mk1 light metering question)