The fact that when using the SBC like an reflective meter, but with the lumisphere set in the incident position, gives readings that match the E-P1, is just coincidence. It makes sense though because you say you need to set compensation to 4 and I believe that the SBC comp dial gives filter factor (not stops) so this means the meter will read 25% of the value that it would read with the compensation set to 1. The lumisphere is designed to give the same reading as if you were using reflective metering on an 18% gray card - in other words, when misused as a reflective meter, it should read about 18% of the real value. This is close enough to the 25% given by your exposure comp as to give an almost identical reading. I would not use the lumisphere for reflected light measurements though, since it will give you a 180% (hemispherical) field of view, which won't match your camera FOV (unless using a 180 degree fisheye!).
I'm not going to weigh in on the EP-1 as a light meter debate, but you might find Ctein's discussion of ISO useful. He's an experienced analog photographer and printer, as well as a digicam user. You can find it on TOP at http://theonlinephotographer.typepad...-isnt-iso.html.
Last edited by andrew.roos; 10-29-2012 at 11:08 AM. Click to view previous post history.