| 摘要 |
This invention is directed to a bitelecentric projection optical system very well corrected for various distortions, particularly for distortion (including higher-order distortions) as securing a relatively wide exposure area and a large numerical aperture. The projection optical system according to this invention comprises in order from the object side toward the image side a first lens group having a positive refractive power, a second lens group having a negative refractive power and not including a positive lens, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, a fifth lens group having a positive refractive power, and a sixth lens group having a positive refractive power. Particularly, the second lens group comprises a front lens disposed nearest to the object, a rear lens disposed nearest to the image, and an intermediate lens group disposed between the front lens and the rear lens and having at least two negative lenses, and the fifth lens group has at least seven positive lenses.
|
