I don't think you are missing anything when using the correct polarizer
for your meter or when using Auto Mode on one of the models with a
partially silvered mirror with a linear polarizer.
The question was about a specific, unusual, situation. It was about
metering on an OM-4 without the polarizer (because it's the wrong type
for the meter), adjusting the Spot Mode shutter speed using exposure
compensation for the filter factor, mounting the polarizer and shooting
the picture. In that case, the meter will include the specular
highlights, polarized skylight, etc. in its exposure reading. If
exposure compensation is then applied only for the ND factor of the
filter, yet it also removes additional, polarized, light from the image,
the result will tend to be underexposed. A picture with very little
polarized light in the scene will be correctly exposed. One with bright
sun reflecting off a large expanse of water, for example, where the
specular reflections account for a large portion of overall scene
brightness, will be quite underexposed.
Moose
Piers Hemy wrote:
I see your point Moose, and have thought long and hard about it, but I think it
is not relevant (though clearly correct) to say the factor varies.
Sure, a polarizer will have a variable effect on the average meter reading
(ignoring for the moment the OM-4 semi-silvered specifics). But in removing
specular highlights from the average meter reading (using a polarizer), surely
all you are doing is eliminating what would otherwise be underexposure of the
rest of the frame? Of course, you would then lose the detail in the reflected
highlights - but if you wanted the detail in those highlights, you wouldn't
have used a polarizer in the first place.
Do you see my point?
What I am missing?
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