ROBERT MILLER, a lobsterman from Beals Island, moonlights as an artist in the tradition of John Marin. Or maybe it’s the other way around — Miller may well be an artist first, a lobsterman second. Either way, he shows his work in a quick exhibition, from 4 to 8 p.m. Friday at the Old Schoolhouse, 13 Cranberry Lane, Jonesport. That’s a long way from Portland and southern Maine, but if you’re headed that way on Friday, the exhibition will be well worth your time. For directions or more information, call 497-2457.