Sharpest iris setting for X70?
 

Anyone figured out what aperture value is the happiest on the X70/CX900/AX100, providing the sharpest picture? Also, anyone figured out what the limit is on closing down the iris before you get diffraction or other image quality robbing artifacts?

On my JVC 790 at work, if you close the $13,000 Fujinon HAs18x4.2BERM past f4.0, the picture begins to turn green/yellow, and contrast begins to fade! If you try to white balance at anything other than wide open, your picture turns blue when you open up the lens! It's quite dramatic.

I shoot at night, so the lens on my camera stays locked at f2.8-f4.0.

Paul