Thus, at any given wavelength, larger telescopes suffer least from the effects of diffraction. Radio and space-based telescopes do not suffer from atmospheric effects, so their resolution is determined by the effects of diffraction. Most modern telescopes now use charge-coupled devices, or CCDs , instead of photographic plates to collect their data. The field of view is divided into an array of millions of pixels that accumulate an electric charge when light strikes them. CCDs are many times more sensitive than photographic plates, and the resultant data are easily saved directly on disk or tape for later image processing.
Radio telescopes are conceptually similar in construction to optical reflectors.
However, radio telescopes are generally much larger than optical instruments, for two reasons. First, the amount of radio radiation reaching Earth from space is tiny compared with optical wavelengths, so a large collecting area is essential. Second, the long wavelengths of radio waves mean that diffraction severely limits the resolution unless large instruments are used. In order to increase the effective area of a telescope, and hence improve its resolution, several separate instruments may be combined into a device called an interferometer. Using interferometry , radio telescopes can produce images much sharper than those from the best optical equipment.