The x-ray telescopes consist of x-ray reflecting mirrors and focal plane
detectors. This is a conceptualization of a conical thin foil x-ray mirror.
X-rays are electromagnetic waves with extremely short wavelength. Total
reflection takes place for x-rays only when incident rays graze the reflector
surface. Because of the small grazing angle of incident x-rays, the effective
area for a reflector to receive x-rays is much smaller than the whole surface
area of the reflector. The x-ray telescope on board ASCA increases the total
effective area with the use of about 100 thin foil reflectors.