Re: light meters

----- Original Message -----
From: "Barry Kleider" <bkleider@sihope.com>
To: "alt-photo-process-l@skyway.usask.ca"
<alt-photo-process-l@sask.usask.ca>
Sent: Tuesday, March 08, 2005 5:57 PM
Subject: light meters

> Does anyone have suggestions/recommendations on light
> meters? (What
> features you look for and price)
>
> I'm using an old Polaris and I'm thinking it's time to
> upgrade.
>
> I've also got an old (very old) Weston that belonged to my
> grandfather.
> No idea how to work it.
>
> Barry
>
    I think there may be a Weston handbook on the web
somewhere.
    The most common older model is the Weston Master II,
built in the mid to late 1940's. It was followed by the
Master III, which is almost identical but used ASA speeds
instead of Weston speeds. Almost all Westons work the same
way.
    ISO speeds can be used on meters calibrated in Weston
speeds by using the Weston number next lower than the ISO
number, i.e., for ISO-100 film set the meter for Weston 80.
Now, having said this it seems that Weston speeds probably
had a 2X safety factor that the Weston meter took out. So,
to get the meter to agree with a modern meter you have to
set the speed to the Weston number next lower than half the
ISO speed.
   You can check the cell for degration by reading a light
value that you can read on both high and low scales. The
reading should be the same within a very small amount.
Degraded cells read low for bright light so a bad cell will
read low for light near the top of the meter scale. This is
true of all meters using Selenium barrier cells. If the
meter reads very low on both scales, or is irregular, press
down lightly on the lens over the cell and move it around a
little. Watch the meter, at some point it will begin to read
normally. Evidently the contact between the cell and the
mounting becomes slightly corroded with time. Moving the
cell around a little will usually fix it. The mounting is a
spring contact. The meter movement is quite reliable. If the
meter seems sticky you can usually clean the pointer
bearings by simply moving the zero adjuster back and forth
and finally setting it to zero. Weston was in the high
quality meter business so their indicator meters are quite
trouble free.
   Be careful making readings because the cell has a rather
wide acceptance angle (on the order of +/- 60 degrees) so
its easy to get too much skylight into a reading.
   The markings of the meter are to indicate acceptable
exposure ranges for B&W and color films. The A and C
markings are the range of color transparency film (+/- 2
stops), the U and O markings are the limits of B&W film, at
least for pinting, 8 stops (U is underexposed, O for
overexposed).
    The very first Weston meters had a B for the center
where the pointer is.
    The film speed setting dial is locked. The lock button
the small chrome button at the side of the calculator
adjacent to the neck strap loop.
    The Weston meter is useful for close up readings to
determine brightness ratios. The design of the calculator
helps to translate these into optimum exposure. For distant
readings the meter integrates the brightnesses, as do all
reflection meters, but, again, watch out for the wide
acceptance angle and false readings.
    You do not need a gray card to compare the meter with
another reflection meter. Any surface that is uniform will
do. There are no adjustments in the meter. If the cell is
good and the meter not damaged it will be accurate.
  The error from a degraded cell is about one stop for a
reading near the top of the scale. More damage results in
very low readings but I've seen only one Weston meter like
this. Selenium cells are sensitive to excessive head and
excessive moisture. Weston had a proprietary method of
sealing the cells which seems to have been quite effective.
The are much more likely to be in good condition than the
cells on comtemporary General Electric meters. The large
size of the cell gives them relatively high sensitivity for
a Selenium meter.
   There was an indident light adaptor available for Weston
meters. This is in the form of an inverted cone which is
nearly identical to a hemispherical surface. The later
version of the adaptor could be fitted with the light
attenuator flat in either position, the earlier version came
with a neutral density filter to get the the "high" range
with the flap in the low range position. When this
multiplier is inserted in the meter it presses against the
tabs under the flap and shifts the meter mask to the correct
scale. The "Invercone" incident light adaptor fits on top of
it. Again, this multiplier is not necessary for late version
Weston meters.
  The calculator is virtually the same for all models and is
used in the same way.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com