The best-known is probably the Hubble Space Telescope , which operates at optical frequencies.

ECONOMIST: Telescopes are getting bigger, better and less tangible

Some experts in the field seriously question whether it is possible to develop materials capable of perfect lensing at optical frequencies.

BBC: Last Updated: Monday, 8 March 2004, 09:03 GMT

The extent of the problem, at least at optical frequencies, has recently been catalogued by Pierantonio Cinzano and Fabio Falchi at the University of Padua, Italy, and Christopher Elvidge at the National Geophysical Data Centre in Boulder, Colorado.

ECONOMIST: Going, going, nearly gone

"Theoretically if you construct the elements we've made at terahertz frequencies, make them even smaller and then scale them up to optical frequencies, you could have perfect lensing at those frequencies, " said co-author Dr Willie Padilla of the University of California, San Diego.

BBC: Last Updated: Monday, 8 March 2004, 09:03 GMT