Nice work, Lester! The 24 f/1.4 is a ripper lens, isn't it?
I like Samir Kharusi's approach to measuring the sky fog because it's quick and easy - i.e. point the lens in a dark region near zenith and do a few test exposures to work out what exposure time would be needed for a middle-histogram sky fog peak at ISO 800 and f/4. He's also provided a translation scale between the exposure time and mag/sq arc sec for a Canon 1Ds.
http://www.pbase.com/samirkharusi/image/37608572