| 摘要 |
PROBLEM TO BE SOLVED: To provide a macro lens system specifically designed for use with medium format SLR cameras, which offers a longer back focus and yet is well corrected for aberrations over a wide shooting range from infinity to 1x magnification and is of an inner focus type having a view angle of around 38-43 degrees.SOLUTION: A macro lens system comprises four lens groups having positive, negative, positive, and negative refractive power. When shifting focus from an infinite shooting distance toward 1x magnification shooting distance, a first lens group is stationary relative to an image plane while a second lens group and a third lens group move in an optical axis direction. A fourth lens group comprises three lenses which are, in order from the object side, two negative meniscus lenses, each having a convex surface on the object side, and a positive meniscus lens having a convex surface on the object side, where the three lenses are separated by air spaces. The macro lens system satisfies the following conditional expression (2): -1.4<f/f<-1.1, where frepresents a focal length of a lens located on the most object side in the first lens group, and frepresents a focal length of the entire system when shooting at infinity. |
