A microscope accessory uses symmetrical pairs of identical parabolic mirrors as an imaging optic to map a specimen plane with a remote focus. A mask at the remote focus defines at least one measuring area for making spectroscopic measurements while a separate viewing system simultaneously provides a wide field of view of the sample at higher magnification. The sample aperture, defines as 2T sterradians of solid angle surrounding each side of the specimen plane, is multiplexed between and among different functions--such as spectroscopic measurements and visual observations. The high numerical aperture possible using identical symmetrical aberration canceling (ISAC) optics facilitates the aperture multiplexing which has particular advantage in making reflectance measurements without any need for a significant loss of throughput efficiency.