Hans-Juergen wrote:
: I find your explanation absolutely logic
: in the case that spot-mode gave HIGHER values (indicating shorter speed)
: for measuring an area with no lens-caused fall-off. An average
: measurement including seemingly "darker" zones because of lens-caused
: fall-off should indicate indeed a less average light-value. But I get
: instead indications for lower speed, means less light at spot...
I think it may have something to do with the accuracy of the led shutter speed
indicator and the extreme sensitivity of the light meter of the OM-4Ti. Although
the shutter speed in Auto mode can be continuously changed, not even limited by
1/3 stop intermediate values, the LED's only have a 1/3 stop accuracy. If you
take a spot reading, the light value (LV) is stored, the shutter speed is
calculated and rounded to the nearest 1/3 stop shutter speed value which is
indicated. You can also be sure that this will be the value that will be used.
With averaged metering, the calculated value may differ within +/- 1/3 stop of
the indicated value which is emphasized by the last led which continuously
blinks indicating that what you see is within 1/3 stop accuracy of what you'll
get. That is, of course, if the light value doesn't change during exposure...
Try this: on a cloudless day, mount a telelens on the body, pull out the hood to
avoid side lighting effects on the front lens, mount the camera on a tripod and
aim it at a completely even lit structureless subject like a wall, tabletop, or
better yet, a neutral grey card, from a very short distance like 10 cm. from the
hood - ignore focus. When you see the last led flicker, try to steady it by
fine-tuning it with the aperture ring by setting it to intermediate F values.
You will see that it is almost impossible to completely steady it. Now if you
press the spot button, even under these very controlled conditions sometimes you
will see that it is 'spot on' to the indicated average value, and sometimes that
it is 1/3 stop below.
The bottom line is that this behavior is normal for the 4Ti and that if you
really want a controlled shutter speed that serves as a base for a 1/3 stop
bracketing series on slide film, you should use the spot meter, memo lever and
exposure compensation dial.
hnz
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