Dave Buyens wrote:
> 2. The moon is sunny 16 exposure, being in direct sun.
This is true, but the situation isn't quite that simple, for two reasons:
1. The moon's reflectance varies with phase, and depending upon which
model you believe, the reflectance decreases from about 15% at
opposition to about 8% one day before or after the full moon, and to
about 2% for a quarter moon. The brightness decreases by about 1/3
step at 4 hours before or after the full moon.
2. Earth's atmosphere absorbs light, and the absorption is much greater
near the horizon than at zenith. At zenith, the air mass is one (0.4
step loss), but at the horizon, the air mass is about 38 (15.4 step
loss). Local atmospheric conditions (temperature, pressure, and
contaminants) can cause values at the horizon to vary by several steps.
It's possible to calculate the moon's luminance for a given phase and
altitude, but the values are estimates at best. With an 840 mm effective
focal length, it should be easy to meter the moon with the EOS 3's
spotmeter.
Even with the 840 mm focal length, the moon occupies only about 5% of the
image area, so that unless the sky is completely dark, the exposure
probably should favor the landscape:
1. Before sunset, the foreground usually is brighter than the moon, so
determine exposure as if the moon weren't there.
2. During twilight, measure the sky near the moon, and set the exposure
somewhere between the meter reading and one step under. Sometimes the
moon-sky contrast is a problem; meter the moon to ensure that it won't
be overexposed. If the contrast is too great, one approach is to make
two exposures in rapid succession: one for the landscape and one for
the moon, and combine them digitally. A D60 would be helpful here ...
Jeff Conrad
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