Elliott toroid camera

Where a more intense spot focus of fairly monochromatic X-radiation is required than is available in either a Franks or a mirror-monochromator camera, an Elliott toroid camera can be used [4]. This camera uses a gold-coated mirror distributed on a toroidal surface, as shown in Fig. 11, to bring an anulus of X-radiation to a focus. 

Figure 11. The Elliott toroid camera. Rays are brought to a focus by the toroidal mirror in this figure the focal length has been considerably exaggerated, normally the radius of curvature of the mirror is 20 m.

---