Comparison of the [O III] λλ 4959,5007 lines with the [O III]λ 4363 line. These lines are produced by the interaction of the SN ejecta with circumstellar material. Due to the occulation of the CSM by an optically thick SN ejecta, less of the “backside” of the CSM is seen. The velocities of the CSM shell (v_CSM), the photospheric velocity (v_FeII) and the maximum velocity of the ejecta (v_max) are indicated.