The VIR series FT-IR spectrometers are designed with flexibility in mind, providing various configurations for the laboratory, the field and customized applications. For even greater flexibility, external connection optics allows the user to install up to three different attachments in one system, selecting the most appropriate application accessory by simply switching the PC controlled optical configuration. A further extension of application capabilities can be achieved by integrating the universal optical base to configure a freely customized configuration by simply placing optimized optical components and sample holders onto the base. Thus even a large sample or an attachment which cannot fit in a standard sample compartment can now be utilized without compromise.