Bright-field (BF)and dark-field (DF)are the most commonly used examination modes. BF OBJECTIVE OR.IECT CONDENSER- 一APERTURE一= 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: 77