The development of improved techniques has made possible a new series of cyclotron resonance experiments on Cu which gives more accurate and extended information on electron cyclotron masses. New orbits which have been observed and measured include a limiting point orbit, orbits extending through three and four Brillouin zones, orbits whose centers are neither at the center nor edge of the zone, and orbits observed with the magnetic field tipped at large angles (up to 80°) with respect to the crystal surface. The neck orbit has been observed and measured with the field along the  direction. The cyclotron mass ratio for this orbit is 0.46. Certain discrepancies and puzzling aspects of earlier data have been clarified and the present data are in excellent accord with de Haas-van Alphen and magnetoacoustic data on the geometry of the Fermi surface. The principal cause of difficulties in the former experiments has been shown to be some perturbations of the absorption spectra of cyclotron resonance when the applied magnetic field is tipped as little as a fraction of a degree with respect to the metal surface. These effects are responsible for the phase shifts in the cyclotron resonance series reported earlier, as well as for the rapid changes in measured cyclotron masses which occurred in certain regions of field orientation. Although these effects are not understood in all details, their principal causes are fairly clear, and the effects can be avoided by maintaining the field accurately parallel to the sample surface.