[rollei_list] Selenium Light Meters
- From: Marc James Small <marcsmall@xxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Tue, 07 Oct 2008 20:26:02 -0400
At 07:07 PM 10/7/2008, Carlos Manuel Freaza wrote:
>I agree with you a bout the selenium cells for lightmeters, they are
>very good, however it seems they are no longer used for new
>professional lightmeters.-
Carlos
If you've not realized this, I am a huge fan of
selenium meters. In the end, selenium more
closely matches the response patterns of chemical
films than do later substrates such as CDS or SPD
or Gallium Arsenide. The problem is that the
later substrates are photo-reactive -- they
display RESISTANCE in line with the amount of
light they receive -- while selenium is
photo-voltaic -- it produces a current in line
with the amount of light it receives. Thus, the
later substrates require a battery to run a
current through the substrate and the resistance
is measured to produce a reading. With selenium,
the current produced engenders the reading.
Selenium cells produce a VERY low amount of
electricity. Thus, they require a very broad
acceptance angle (they read a LARGE area) and
require a complex mechanical linkage to magnify
the low current reading to a form capable of being placed unto a dial.
Another problem is training and age. Us
old-timers -- I am pushing 59 -- who came up with
selenium meters know how to use them. The rest
of you youngsters do not. An accurate reading
with selenium requires that the photographer save
the meter or camera about a bit to obtain an
average reading. And selenium meters, due to the
very low current they produce, are not capable of
working in low-light conditions.
I love the meter in my Leitz M6 Wetzlar and that
in my Rollei 2.8GX and the Kiev-88 Meter Prism I
use on my Hasselblad 2000 FC/M. But my standard
meter remains my father's 1939 Weston 715,
overhauled every decade or so by George Milton at
Quality Light-Metric. Heck, I even have a
Prewar Metrawatt Leica-Meter 60 which is a really
neat device to use on my IIIc.
I had been aware of the purchase of Metrawatt by
Gossen and thanks, Carlos, for reminding me of this.
Marc
msmall@xxxxxxxxxxxx
Cha robh bàs fir gun ghràs fir!
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