| 摘要 |
<p>In order to reduce variations in aberrations, particularly variations in chromatic aberration, and correct aberrations favorably while obtaining a significant magnified observation effect in an object lens for an endoscope, this object lens is configured such that focusing is performed from the farthest-point object to the closest object by moving, along the optical axis (Z), at least one negative lens group except for the lens group closest to the object side. One of the negative lens group(s) that is moved at the time of focusing comprises a cemented lens in which a positive lens and a negative lens are cemented in this order from the object side. The cemented surface of this cemented lens has a concave surface facing toward the object side. The object lens satisfies conditional expressions (1) and (2): 1.1<=ft/fw...(1); and 0<nun-nup...(2). Here, ft and fw are, respectively, the focal distance of the entire system at the time of focusing on the closest object and the farthest-point object, and nun and nup are, respectively, the Abbe number of the negative lens and the positive lens of the cemented lens.</p> |
