----- Original Message ----- From: "Robert Lilley"
<54moggie@xxxxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Sunday, March 18, 2007 6:05 PM
Subject: [rollei_list] An ebay explanation
A man has a Weston Master V light meter for sale on eBay. I ask him
if the
meter worked and if it is comparable to other meters - this is his
reply:
Hello Rob, Each make of equipment that measures light differs from
the next.
Although the Linhof and Weston both use selenium cells the angle of
acceptance chosen by the manufacturers will not be the same. The
Linhof has
a fixed lens and shutter as did the Rolleiflex. The Contax measures a
much
smaller area. All shutter speeds are nominal ( 1/100th of a second on
one
shutter may really be only 1/80th and f/2 may only be f/2.2 ). In such a
case test exposures should be made and the negatives carefully
evaluated to
arrive at the best platform from which to work. The Weston caters for,
amongst many others, shutter times of 1/60, 1/80, 1/100 and 1/125 so in
practice it may be best to use the aperture indicated for 1/80th even
though
your shutter is set at 1/100th. Black and white and colour negative
materials have greater lattitude than transparency film and are more
able to
take slight variations in their stride. Transparencies need that
extra care
so that getting to really know your equipment is so satisfying. Buy
it and
enjoy it! Regards,
So does it work?
Rob
The usual fault in a Selenium cell meter is that the cell becomes
insensitive for high light levels but reads OK for low levels. This
can be tested for in any meter that has a high and low range with an
overlap. A reading taken in the overlap region should be identical in
the two ranges. The error is on the order of about one stop but can be
larger. The only cure for this is to replace the cell. Damage to the
cells can come from overheating or from a breakdown of the seals
allowing moisture to get in. Weston cells seem to be reasonably long
lived.
A problem specific to Weston meters is poor contact between the cell
and its contacts. This can often be cured by pushing in on the cell
lens a bit and turning it. I have cured meters that read low all over
and meters that were intermittant this way.
Some of this fellows answer makes some sense but he is waffling. It
is not true that different meters will read differently on the same
light, although some care must be used in comparing them. Reflected
light meters should be compared using a highly diffuse surface large
enough to fill the acceptance area of the meter. It does not have to
be 18% gray for comparison purposes, plain white will do. The idea is
to check by comparison not to get an absolute calibration.
I have A Gossen Luna-Pro, and a Sekonic Studio Pro (now sold under
another name), both read identically for both incident and reflected
light. I also have a couple of ancient meters, a GE PR-1 and a Weston
Master II. The GE reads the same as the Luna-Pro. Now, the Weston
meter, which has a good cell by the above range comparison test tends
to underexpose. I think this is because the Weston speed system for
which it is calibrated must have had some sort of correction factor.
Weston speeds were derived by a different method than either the old
ASA system or the current ISO system but, in general, the calculator
correction is to use 80% of the ISO speed. I find I get correct
readings by using about half this. I've found this true of some other
Weston meters calibrated in Weston speeds. Its probably NOT true of
Weston meters calibrated in ASA or ISO speeds.
I am telling you more than you want to know. If the meter passes
the range comparison test its OK and probably calibrated as well as
when it was new. If not give it the go by, new cells can cost as much
as a good used meter.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
