The photographic emulsion technology of the OPERA experiment on its way to find the nu(mu) ---> nu(tau) oscillation

The OPERA experiment (Oscillation Project with Emulsion tRacking Apparatus) is a long baseline appearance search for @n_@m->@n_@t oscillation. A pure @n_@m beam from CERN is sent to the 730 km far away LNGS underground laboratory in Italy where th e OPERA detector is located. The charged current @n_@t interaction will produce a tau lepton which then can be identified according to its decay topology. The detection of the tau requires a high resolution of the active detection material because of the short lifetime of the tau. Nuclear emulsion films are the most suitable detector material capable of fulfilling this requirement. This article is going to review the status of the experiment, the detector and the way to find the @n_@m->@n_@t oscillation b y observing the tau lepton. Special emphasis is put on the emulsion detection technique.