>>> The experience I've had with Provia 100F in the U.S. Pacific Northwest,
>>> where it is overcast 9 months out of the year, is that it is actually best
>>> when overcast. If I take pictures of a forested scene that is hundreds of
>>> feet away (e.g. a waterfalls with surrounding moss-covered cliffs) with a
>>> blue sky (but no direct sunlight), there is a discouraging blue cast to the
>>> whole scene. (I can fix most of this in the scanning process.)
This is because the ambient light comes from the blue sky, which is, er,
blue. So you get a blue cast, just as if you had used a giant blue softbox
(which is what the sky is). You will see the same thing in shadows on a
sunny day since they are also illuminated by blue ambient light. Sunlight,
by contrast, is much warmer.
> The colors are much more realistic if the same scene is taken with an
> overcast sky.
This is because you're using a big WHITE softbox.
> Also, for closeups deep within the forest, even with a blue
> sky, colors are great with no blue overcast. Does anyone have an explanation
> for this behavior?
Yes, in this case the deep shadows are illuminated not directly by the blue
sky but indirectly by light reflected from leaves, bark, ground etc which
largely removes the blue cast, since they tend to reflect mainly red and
green light (bark and leaves!) -- a sort of very dim organic muddy softbox.
You can use this to your advantage when shooting BW as a blue filter will
generally lighten shadows and a red filter will darken them.
It's all covered in Ansel Adams THE CAMERA and THE NEGATIVE, incidentally.
--
Johnny Deadman
http://www.pinkheadedbug.com
