<P> A collimator is a device that narrows a beam of particles or waves . To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spatial cross section of the beam to become smaller (beam limiting device). </P> <P> An English physicist Henry Kater was the inventor of the floating collimator, which rendered a great service to practical astronomy . He reported about his invention in January 1825 . In his report, Kater mentioned previous work in this area by Carl Friedrich Gauss and Friedrich Bessel . </P> <P> In optics, a collimator may consist of a curved mirror or lens with some type of light source and / or an image at its focus . This can be used to replicate a target focused at infinity with little or no parallax . </P> <P> In lighting, collimators are typically designed using the principles of nonimaging optics . </P>

What are the shutters that make up the collimator made of