William, that would make sense if the focus screen would change it's
behavior as you changed the exposure mode or transmitted more light as
you changed the aperture. I think... shitty week, here.
As I was raised believing, there is no better exposure than the stopped
down metering just before the actual exposure of the film/ sensor. Those
days there were some lenses that would not close their apertures
properly, most of them cheapo samples with poor tolerances.
Issues were delays (lens still closing while the film was being exposed)
and real aperture not equal to the ring values (either incorrect
adjustment so the indicated 2.8 was actually closer to 2.0 and the
difference to the lens wide open would be less than it should be, or low
quality lenses promising fast apertures they didn't really have - so
again the difference from the 2.8 to the real 2.0 wide open would be
inferior to the promised but not delivered 1.7). But those issues would
be prevented by stopped down metering just before the exposure - and
later by real time metering from the film as in the Lx and some OM
Olympus cameras.
Facing over or underexposure with open lens metering I would blame the
wrong aperture as closed or the wrong assumption of the maximum aperture
of the lens. I can't think of focusing screens with active, light level
adjustable transmission index.
LF
William Robb escreveu:
In response to this question:
"I was informed that the camera is a little bit under-exposed, but I
want to
know how much. That is, if I set the EV compensation, but how much (1/3?
1/2?) should I set so that I can get normal exposure?"
This answer was given:
"Well, regarding the exposure problem, let's say it's related to the lens
used.
For f/3.5-5.6 lens, exposure will be quite good.
But with fast lenses, you'll have a variable amount of underexposure...
- f/1.4 needs about +1 1/2ev
- f/2.8 needs about +1ev
and so on...
This is due to the fact that the focus screen does not respond in a linear
way to the aperture of the lens...
You should have a direct relation between shutter speed and aperture (i.e.
going from f/1.4 to f/2 should halve the shutter speed, going from say
1/1000 to 1/500).
But with the original k20 focus screen, this relation is not respected
(going from f/1.4 to f/2 won't halve the speed).
Note : I'm talking about using actual, stop-down apertures.
For A lenses, the exposure is mesured wide-open, then calculated for the
given aperture you want to use, so selecting f/2 will always gives half the
speed of f/1.4.
BUT the wide-open reading will be underexposed by the 1 1/2ev mentionned
above, so the lens will always underexpose, whatever aperture you're using.
Using an old lens (with aperture blades actually moving when you select an
aperture on the lens), you'll see that closing one stop won't halve the
speed.
You can lessen this behavior by using a LL60 screen (from the *ist line).
They are fully compatible with the k10/k20, and lessen the discrepancies to
the point where you won't really need to compensate the exposure anymore."
--------------------------------------------
I'm not seeing where the answer could possibly be correct, but I thought
I'd
post the whole thing here, hoping to generate some discussion.
This comes from that forum thang, where I managed to get a 2 point
demerit yesterday for telling a guy to fuck off.
Godders, I must just have been having a shitty day yesterday...
William Robb
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Luiz Felipe
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