A 34'x34' field centred on the spiral galaxy M 81 has been searched for emission-line objects using the prime focus wide field camera (WFC) of the 2.54 m Isaac Newton Telescope (La Palma, Spain). A total of 171 candidate planetary nebulae (PNe) are found, 54 of which are in common with the ones detected by Jacoby et al. (1989). The behaviour of PNe excitation as a function of galactocentric distance is examined, and no significant variations are found. The PNe luminosity function is built for the disk and bulge of M 81, separately. A distance modulus of 27.92 +/- 0.23 mag is found for disk PNe, in good agreement with previous distance measurements for M 81 (Jacoby et al. 1989; Huterer et al. 1995). Based on observations obtained at the 2.5 m INT telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofisica de Canarias.