Ok I'll have a go at this. At 800ASA try a 30 second exposure at f8. that is usually enough to show a light-polluted sky but it does of course depend on induvidual circumstance such as brightness of the lighting and the amount of cloud. The picture will come out dark. If you want brighter results you will need to expose for much longer. I reckon a moonlit night and a two minute exposure at f8 gives something looking like daytime. Regarding correcting for reciprocity failure I use the very general rule of allowing an extra stop, which works ok for exposures of a few seconds.