| 摘要 |
PROBLEM TO BE SOLVED: To reduce burden imposed when a fours is detected by eliminating need for mechanically or optically aligning returning light reflected from a testee body and a photodetector. SOLUTION: This focus detector is provided with a light source for detecting a focus 9, optical systems for detecting a focus 4 and 10 for condensing luminous flux on the surface of the testee body 5, a beam splitter 14 splitting the luminous flux reflected on the testee body 5 into two, and the first and the second photodetectors 19 and 20 respectively receiving the split luminous flux. The first photodetector 20 is arranged at a position more separated from the testee body 5 than the convergent point of the luminous flux emitted from the light source 9 and reflected on the testee body 5. The second photodetector 19 is arranged at a position being closer to the testee body 5 than the convergent point of the luminous flux emitted from the light source 9 and reflected on the testee body 5. Then, the first and the second photodetectors 19 and 20 are the two-dimensional photodetectors. |
