Bob_McBob said:
It's not the metering range that's the problem (for instance, ISO 3200, 1/15s, f/2 is still EV1), but rather the way the meter is mechanically coupled to the shutter speed dial.
That's true -- but just for the record (or for any newcomers reading) it doesn't mean that the meter would read in lower light if the mechanical coupling had been designed differently. The coupling is actually a designed-in feature to warn you when you get below the meter's inherent capabilities.
All meters have a low-light sensitivity limit -- once the number of photons hitting the meter cell falls below a certain threshold, the meter no longer provides accurate readings.
Some older meters that used simple circuitry just kept reading down below this accuracy threshold, so you might THINK you were getting accurate exposures in ridiculously low light even though you really weren't!
To prevent this, meters with more sophisticated circuitry incorporate a lockout that displays a warning when the light gets too low for accurate readings. On many camera meters, this is done via an electrical or mechanical coupling to the exposure controls: when you set a film speed/shutter speed combination that would require a reading below the meter's threshold, the meter disconnects.
At this point, someone who's been following this carefully is going to say, "But the meter disconnects at the same shutter speed, no matter whether I'm using an f/1.4 lens or an f/4 lens! If the problem is low light levels, why can't I keep going lower when I use a faster lens?" The reason is that with a stopped-down meter (like the ones in the Bessa RFs) the meter circuit has NO idea what kind of lens you have on the camera or what aperture you've set! The designers have to choose a cutoff number at which it's
likely you'll exceed the meter's limits, regardless of what lens you're using.
