| 摘要 |
In an optical system wherein optical systems corresponding to optical discs of differing standards are combined by sharing some parts, in the case that a skew adjustment is optimally carried out on the objective lens for one medium, the difference in the best tilt angle due to the coma aberration occurring for the other medium is reduced. The position of the second light source in the optical axis direction is set on the side that is farther away from the objective lens than from the position where the wave front aberration becomes of the minimum. Thereby, the amount of increase of the coma aberration is reduced when the skew angle of the objective lens changes in accordance with the second optical information recording medium. In addition, more preferably, the light source is set at the position where the coma aberration does not change in accordance with the skew angle of the objective lens . This position is located between the position where the wave front aberration is of the minimum and the position where the optical system becomes an infinite system so that the increase of the dimensions of the optical head can be controlled and the increase of difference of the working distances can be controlled in accordance with the two optical information recording media. <IMAGE> |
