A simple Connectorized U-bracket allows setting the desired intensity attenuation or spectral filtering by inserting the appropriate mini filter from the set.
The inserts can be fitted with attenuating filters or spectral filters made from a variety of glass materials. Ex: UBI_Semrock_FF01-474/23-25, UBI_Chroma_ET470/40x
NA converter modifies the geometry of an input fiber guided light beam. Both the numerical aperture and the beam diameter are affected: their product is a constant, so called Lagrange invariant.