A multi-spectral imaging system utilizing tunable optics is disclosed. Various disclosed systems include a tunable optical filter coupled to a broadband imaging system. The tunable optical filter allows discrete infrared wavelengths to pass to the broadband imaging system so that monochromatic infrared images of a scene may be captured. An image processing system may process selected monochromatic infrared images by using a ratio technique to generate an emissivity-independent thermal image of the scene. The tunable optical filter may also be used to adjust a quality factor and control an amount of radiated energy that is passed to an image sensor of the broadband imaging system thereby acting as an aperture to account for both low and high radiance portions of the scene.