I've got all the mental ray settings (mr Sun, mr Photo. Exp. Control, mr Sky, and mr Physical Sky w/ a jpg of a sky and clouds attached) turned on at default settings (i think) and I still get a sky that fades from basically light hazy to black as it goes up. The map isn't showing up, and the rendering as a whole is darker than it should be.
I followed some tutorial about making taking a new material slot. Then...Get Material-->mr Physical Sky. From that material's settings, I checked "use Custom Background Map" and found my sky jpeg.
I've had that unchecked for a while trying to at least get a decent blueish mr Sky. Since my first post I've at least found that if I bump up the mr Sky and mr Sun multipliers to about 4.5 that I get a blue sky, but it's a pretty unrealistic (and obviously uncloudy) deep blue sky.
I found another solution...get your company to purchase the ultimate RPC package and get your choice of near perfect skies! The only thing is, mental ray takes the "average" of the surrounding color and bounces that color light around the scene inside your environment "bubble." The skies are really good.
I've had to trick it by selecting a white ground plane (which will bounce good white light around) rather than green grass (which turns my scene/sky greenish- it looks like a tornado is coming!)
Welcome my friend!But i don't satisfied this sky problem.If they can't show custom background ,they don't allow custom map background with daylight system(mental ray).
I know this is gonna sound whack but it worked for me. Go into your exposure panel and change your physical scale to manual and bump it up to about 80,000 to 100,000.