16 Oct
2005
16 Oct
'05
4:57 p.m.
On 10/16/2005 at 11:36 PM ard at p850ug1.demon.co.uk wrote:
To go OT for a momnet, a lot of 1950's/1960's
cameras used a mercury cell
to power the exposure meter. The constant voltage meant the circuit could
be very simple (just the CdS photoresistor, the mercury cell, a
microammeter movement and a couple more resistors, generally). Now that
such cells are unobtainium, there are various kludges, some of which work
better than others, but it's still a pain.
Modern silver-oxide batteries have very stable voltage-vs-discharge
characteristics. My 1960's Nikon F2 Photomic uses a pair and does just
fine.
http://www.sony.net/Products/MicroBattery/sr/
--Chuck