A system for measuring thermal degradation of composites includes a cylindrical body; a bottom cover having a lower central aperture; an upper concave mirror facing the bottom cover with an upper central orifice concentric with a central axis of the body; a lower concave mirror facing the upper concave mirror with a lower central orifice concentric with the central axis; a source of actinic radiation between the upper concave mirror and the lower concave mirror on the central axis to direct actinic radiation through the lower central orifice and lower central aperture; and a camera with an image sensor positioned concentrically relative to the upper central orifice; wherein the bottom cover is adjustable relative to the cylindrical body to provide a focusing function for the image sensor by varying the distance from the lower central orifice and the upper reflective surface.