| 摘要 |
PURPOSE:To eliminate the correction error of initial values in the relative positional relation of a light quantity distribution and to improve accuracy at which the focus of an objective lens is detected by eliminating a shape difference in a light quantity distribution or the level differences of light quantity, which are produced by luminous fluxes transmitting varying areas in the pupil of the objective lens and which are included in the distribution of the light quantity of a pattern member. CONSTITUTION:An extracting means 22 is provided which extracts only the electrical signals indicating the pattern member's light quantity distribution, among electrical signals from photoelectric transfer element trains 16a and 16b, when said distribution is projected to said trains 16a and 16b. Moreover, a correcting and converting means 23 is provided which corrects and converts the relative levels of the electrical signals, as separate photoelectric transfer element trains 16a and 16b, and which supplies them as signals indicating the pattern member's light quantity distribution for calculation performed by a calculating means 24. A shape difference in the light quantity distribution or the level differences of light quantity, which are created by luminous fluxes transmitting varying areas of the pupil of the objective lens and are included in the pattern member's light quantity distribution, is eliminated. Thus, the correction error of initial values in the relative positional relation of the light quantity distribution can be eliminated, and moreover accuracy at which the focus of the objective lens is detected is improved. |
