Feb1-14, 02:05 PM
@ FactChecker: It is nice to be getting a well though out response on this thread. (I like the handle, btw; it makes me stand to attention, mentally.)
That factor of 1/million was probably an overstatement (I'm not sure) But you can go on the evidence of photographic experience. The difference between the reflected light from an object in full sun and in shade (in the absence of light cloud and other reflecting objects) is 'several stops' or a factor of a factor of 1/16 or less. That figure does't actually compare the intensity of light in a 1' solid angle from the Sun and from the sky - which is what I was getting at. The 'stops' figure is based on an integral and so I contend it is an underestimate. But I take your final point, to some extent.
If we assume you are right, and that the overall effect of scattered light from the sky, compared with direct sunlight, on any arbitrary volume of air, the ratio would still be a factor of 1/16, which can hardly be a significant modification of the perceived colour (subjective) of an already very de-saturated Blue. Either way, to me it seems to be a distractor and it is not valid to attribute the ' blueness' to 'blue coming down from the sky' and being scattered.
I am not sure how directly the practice of using a warming filter relates to this. I often tinker with the colour balance in cloudy and shady shots but I think that is due to the absence of the red from the obscured Sun, rather than to any extra blue from the clouds. That's a bit of an open question, I think. The fact that warm means cold and cold means hot, subjectively, doesn't help here. (lol)
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