Bright-field(BF)and dark-field(DF)are the most commonly used examination modes. BF OBJECTIVE OBIFCT CONDENSER APERTURE一= DF ANNULAR STOP-IRIS CENTRAL STOP Figure 1.28 (a)Bright-field illumination:and(b)dark-field illumination in transmitted mode.Shaded areas indicate where the light is blocked. Figures from Leng,pages 26,27. 10 88