I have found with negative film, Sunny 16 is perfect, and my exposures turned out fine. It's gets harder the darker it gets in my opinion. In broad daylight, I find it very effective. I'm in London, and I did the same in Hawaii, results were just as good.
i hope the sun is also calibrated to sunny 16 ,oe,e are in...
The "Solar Constant" bears that name for a reason. The sun's energy output is quite uniform.
The f/16 correlation should be accurate at mid latitudes for subjects illuminated by direct sunlight
without intervening attenuation, like high clouds, haze, smog, etc, and without abnormally high
ground-level reflectivity (sand, water, etc)..
“Wise men talk because they have something to say; fools, because they have to say something.” - Plato
I too have seen inconsistency with the sunny 16 rule in South Georgia. It's mainly sunny 11 dropping to 8. I just attributed it to varying levels of hazyness; humidty, pollen, and polution along with composition. There have been many times when I thought the meter was underestimating the amout of light on a seemingly sunny day but in most cases the meters were right and my eyes were wrong. Gotta get better at reading the shadows and color lightness I guess.