Mirror elements are selectively interposable in the beam paths in a dual aperture microspectrometer system to selectively bypass the aperture element in transmission or reflection modes to increase optical throughput and field of view. The system may be operated in a dual aperture transmission mode or reflection mode and in modes in which the aperture is bypassed before or after the infrared beam reaches the sample. The system may be operated to bypass the aperture both before and after the sample, which may be utilized with an array detector having multiple detector elements in which an image of the sample is formed on the array detector.