The Luna Pro is not a selenium meter. I've forgotten what kind
of cell it has, I think Cds. It needs a battery which no Selenium
meter does. At very low light levels the cell has very slow response
time. My Luna Pro, which I just tested, takes a good minute or more to
settle at the bottom of the high range. When given some time the low
end of the high range reads exactly the same as the high end of the low
range (12).
Selenium meters that are getting aged will have an error of
around a stop or more for the same light level on the two ranges with
the top of the low range tending to read low. This also shows up when
comparing the high end of the high range against a good meter, it reads
low. The meters seem to develop about a one stop error which remains
costant for a long time. Eventually they become very insensitive all over.
BTW, I learned a trick with the Weston Master: These sometimes
become intermittent or read quite low. The cure is often to clean the
internal contacts by pushing in on the cell window and rotating back and
forth several times. Has worked for me a few times.
GE meters seem to have cell problems on all versions. Same
with the original Norwood Director. The Sekonic version seems to be
better. I don't know if Sekonic still makes replacement cells but in
any case they are the wrong size for the Norwood meter.
Try your Luna Pro again but give it a couple of minutes to settle.
On 7/8/2015 4:40 PM, Tim Daneliuk wrote:
On 07/08/2015 06:35 PM, `Richard Knoppow wrote:
The test is to measure light that falls in the overlap range on both ranges.My experience - even with really good meters like Luna Pros - is that they do
NOT match across ranges when the value is at the extreme end of the low range.
These meters are most accurate when they are around mid-deflection of the
needle.
They are highly nonlinear at the ends.
I say this having just completed cleaning, overhauling, adjusting, etc. a
couple of Luna Pros and a Luna Six.
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