On Mar 30, 2016, at 8:49 PM, Wayne Bretl <waynebretl@cox.net> wrote:
Example: suppose direct sun is 5000K = 200 mired; and blue sky is 16000K = 63 mired . This is a difference of 137 mired
On Mar 30, 2016, at 9:33 PM, Uli Zappe <uli@ritual.org> wrote:
2. Calculate the Bradford chromatic adaptation matrix for a white point shift from D160 to D65 (= from the real to the fake sky)
Thanks much to both Wayne and Uli -- between the two of you, those were exactly the answers I was hoping for. In practical terms, it looks like I'll be buying the Rosco 1/2 CTO, 3/4 CTO, full CTO and double CTO filters to experiment with; they have mired shifts of, respectively, 81, 131, 167, and 320. And, of course, the bigger the shift, the less the transmission...stop losses are 0.5, 0.8, 1.1, and 2.1. One of those four should provide the look I think I'm imagining. The 3/4 CTO is as close a match to Wayne's number as is likely to be commercially practical. The 1/2 CTO goes in the direction of Uli's figures, probably overshooting. I think the full CTO might be what I'm envisioning, with an especially blue sky in the Golden Hour. The double CTO would let me experiment with some over-exaggeration. So, thanks again. I'll (eventually) report back with results. (And, of course, I'll also need to balance the luminosity of the two sources, but that's much more straightforward.) Hmmm...just occurred to me that I could maybe adapt this to have some fun simulating alien landscapes with more than one local star in the sky.... Cheers, b&