Roper Industries Inc., of Bogart, Ga., has bought Acton, Mass.-based Acton Research Corp., a manufacturer of precision optical components, spectrometers and spectroscopy systems, for $11 million. Under terms of the agreement, Acton will become a wholly owned subsidiary. Acton had net sales of $10 million in 1997. Last May, Roper acquired Princeton Instruments Inc. of Princeton, N.J., a manufacturer of charge-coupled device cameras. Acton will join Princeton as part of Roper's Analytical Instrumentation Segment.