Abstract: Macroscopic and microscopic samples are imaged through a spectral filter operable into the short wave infrared, e.g., to approximately 3200 nm. The sample is illuminated for reflective, transmissive, fluorescent and/or Raman imaging by a laser or metal-halide arc beam. The filter has tunable birefringent retarders distributed rotationally and stacked in stages leading up to a selection polarizer. Image forming optics and CCD cameras collect the luminance of each pixel in the spatially resolved image, at multiple wavelengths to which the filter is tuned successively. The filter stages have comb shaped transmission characteristics. Two filter stages with distinctly different characteristics can be cascaded, one or both being tunable. The combined transmission characteristic has narrow passbands where the bandpass peaks of the stages coincide and wide free spectral range where the peaks do not coincide.