Rob Dalrymple , Nov 14, 1997; 02:09 p.m.
If I have a correct understanding of what you are trying to do, no compensation or changing of the asa should be necessary. (except to offset for any reciprocity failure) The object is to expose different areas of the frame with each exposure. First shot- you expose for the moon, the rest of the frame is dark (no exposure). with the second shot you expose the rest of the frame, (the landscape) while being careful not to have any exposure in the same part of the frame that your've already put the moon in. Since no part of the film should get exposure on both shots, you shouldn't need to compensate for it.