NEAR MISS ON DEP INVOLVED AN ULTRALIGHT PASSING WITHIN 100 FT VERTLY OR RPTING ACFT.

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DEPARTED MANCHESTER AT XA41Z. AT APPROX XA49Z ON CLBOUT OF 500 FPM PASSING FL110 CLRED TO FL170; ON ASSIGNED HDG OF 255 DEGS; WE ENCOUNTERED AN NMAC WITH AN ULTRALIGHT ACFT. THE ULTRALIGHT PASSED DIRECTLY UNDER US AT LESS THAN 100 FT. MY COPLT; HAND FLYING OUR ACFT; EXECUTED AN INSTINCTIVE PULL; BUT BY THE TIME OUR ACFT REACTED; WE WERE ALREADY CLR. FROM THE TIME WE BOTH VISUALLY ACQUIRED THE TFC TO CLR WAS LESS THAN 1 SECOND. WE WERE TRAVELING AT APPROX 340 KIAS. I RPTED A NEAR MISS TO ATC. I DON'T THINK THERE WAS ANYTHING ELSE ATC OR WE COULD HAVE DONE DIFFERENTLY. EDUCATING ULTRALIGHT PLTS WOULD BE THE ONLY HELP. WE WERE ON AN IFR FLT PLAN IN VISUAL CONDITIONS IN CTLED AIRSPACE. SUPPLEMENTAL INFO FROM ACN 430573: THE CTLR TOLD US THEY WERE PAINTING A TARGET BUT WITH NO ALT. IS IT REASONABLE TO ISSUE AN ADVISORY TO US? I THINK REALISTICALLY TARGETS POP UP FREQUENTLY AND EVERY SIT IS DIFFERENT. WE WERE BOTH AMAZED AT HOW HE FILLED OUR WINDSCREEN AND PASSED UNDER US IN JUST A SECOND OR LESS.