Re: Leica meter MR-4

[pgs@thillana.lcs.mit.edu (Patrick Sobalvarro)]

Whoops, it looks like I've offended you, which I certainly didn't mean
to do.  My mentioning your "alarm" was meant lightheartedly, and I'm
sorry if it came off somehow as insinuating something else.

That said, the argument that the spacings of the meter readings are
not linear and therefore one cannot adjust the meter by a known
reference light intensity is still wrong, for reasons I explained in
my last message.  The only possible problem from nonlinearity arises
if the adjustment screw becomes insensitive when the meter is reading
light, which may or may not be true on the MR-4 -- I don't have one so
I can't check.  My guess, though, is that the adjustment screw
mechanically sets the needle offset, in which case it is very unlikely
that the screw is less sensitive to turning at one part of the dial
than at another.  Note that the screw adjustment can't be adjusting a
potentiometer because it moves the needle even when the batteries have
been removed from the meter.

I don't think it matters that much, and I do think people should use
the procedure you described from the manual.  I sent the message I did
because it occured to me when I read your message that light meters
and their adjusting screws have some interesting characteristics like
monotonicity and the fact that they implement a bijection and that,
because of those properties, linearity can't matter except if the
screw becomes very insensitive when the meter is reading light.  I
thought that was kind of interesting and worth remarking on, but
possibly my notions of what is interesting are unusual.

P.S. So that this message has a little more Leica content, I thought
     I'd mention that I used a flashbulb with my M2 the other night.
     No kidding, a Sylvania #5.  My friend who'd brought the flashgun
     over with his Crown Graphic said (perhaps excessively
     anthropomorphically) that the M2 was probably thrilled at the
     opportunity to fire a bulb when taking a picture -- it probably
     hadn't used its flashbulb terminal in 30 years!