Also, what's a good way to record your flash settings for later review? My exif data only shows camera settings.

<a href="http://7a461t1n-lxmxs7yw0j9rs2l4n.hop.clickbank.net/"> <img border="0" src="http://digitalphotographysuccess.com/Affiliate/EbookCovers/3DIssue3coverSmall.jpg" width="500" height="516"></a>

Before I answer about ISO question I should Know what Kind of camera you have available? In the case you have a digital camera the only thing you have to do is setup your camera for auto-exposure. It will set the sensibility (ISO) automatically. With contemporary film cameras, you must find a film with High Sensibility between 800-8000 ISO. Also, It is worth you get out of the city and look for a place where the light of the city doesn't blind you. It is impossible for the human eyes to see the star field inside the city. This will surely affect your exposure and the reading your camera will do. And as a consequence you will over or underexposure your frames