An X-ray refractive lens, often referred to as a Compund Refractive Lens (CRL), is a fairly new type of device, which has gained popularity in the last few years. An early study showing the feasiblity of such devices may be found in [SKS96]. As the refractive index of X-rays is \(n\approx 1\) a number of lenses, stacked together is usually necessary to bring the focal length to practical values. McXtrace includes a few lens components, which all have slightly different charactertics.