“…Consequently, the total transmission efficiency is reduced if the filter pass-bands only overlap in the spectral range of the edges, thus limiting its use for very small spectral bandwidths. This problem cannot be overcome easily, as it requires either a source with smaller diameters, e.g., point-source like, 19 which may not be available as a high intensity non-coherent light source, or a larger focal width of the collimating lens, which is also not always applicable due to the usually high numerical aperture of the source, which would then result in a low transmission efficiency. Also, the filter dimensions restrict the beam diameter and therefore the collimating lens diameter, which limits the focal length at a given numerical aperture.…”