Three-Group Imaging Lens for Compact Macro Photography

The lens is divided into three distinct lens groups (first with negative power, second with positive power, third with positive power) that can move independently. This segmentation allows the focusing function to be distributed across multiple groups rather than requiring the first lens group to handle the entire focusing range alone, thereby reducing its moving amount while maintaining macro imaging capability.

The patent implements dynamic focusing by allowing at least one of the first or second lens groups to move relative to the others during focusing from infinite distance to life-size magnification. This dynamic adjustment of inter-group distances enables the system to achieve macro capability without requiring excessive movement of any single lens group.

The patent employs a nested arrangement where the first, second, and third lens groups are positioned in sequence along the optical axis with minimized spacing. The lens groups are nested within a compact barrel structure that allows for controlled extension only when necessary for macro focusing, rather than requiring the entire barrel to be long from the start.

The lens barrel is designed with dynamic extension capability that activates only during macro focusing. In the infinite-distance focusing state, the barrel maintains a short length with all lens groups in a compact arrangement. When macro focusing is required, the barrel extends minimally to accommodate the movement of lens groups, thereby achieving compactness in normal use while enabling macro capability when needed.

The focusing function is segmented across multiple lens groups, with the first lens group having reduced moving amount. The second and third lens groups compensate for the reduced movement of the first group by their own movements, ensuring that spherical aberration and curvature of field remain well-controlled throughout the focusing range from infinite distance to life-size magnification.

The patent optimizes the refractive powers and focal lengths of the three lens groups to specific parameter ranges. The first lens group has negative refractive power with a focal length satisfying a specific conditional expression, while the second and third groups have positive refractive powers with their own conditional expressions. These parameter optimizations enable effective aberration control even with reduced moving amounts.