A Toroid mirror comes in the shape of a parabola having a reflective surface such that it can be used to collect or project the energy such as light, sound or radio waves. The key point here is that its focal length is variable and depends upon the angle of the mirror at which it is oriented and the source and detectors are not located on the optic axis of the mirror. Toroidal mirrors are normally used where a beam needs to be focused or folded to remove astigmatism, or for correction of aberrations. Toroid Mirrors are specifically used in Yolo Telescopes and Optical Monochromators.