Compact Imaging Lens with Aspheric Cemented Groups

The lens is divided into multiple lens groups (first lens group with positive refractive power, second lens group with positive refractive power, and third lens group with negative refractive power). Each group is positioned at different locations relative to the stop, allowing the strong concave surface to be placed on the image side while distributing the optical power across segments. This segmentation enables achieving long flange back for optical performance without requiring the entire optical length to be long.

The patent employs a focusing mechanism where at least one lens group moves along the optical axis to adjust focus from infinity to close objects. This dynamic adjustment allows the lens to maintain optimal optical performance across different focusing distances while managing the overall optical length. The movable lens groups enable flexible control of light paths without requiring a fixed long optical length.

By segmenting the lens into multiple groups positioned at different locations, the patent creates space between lens groups and the image plane (long flange back) where optical elements can be inserted. This segmentation strategy provides adaptability for adding filters, polarizers, or other optical elements without requiring a uniformly long optical path throughout the entire lens system, thus maintaining better compactness.

The patent arranges lens groups in different axial positions to create a long flange back specifically in the region between the second lens group and the image plane. This dimensional arrangement provides the necessary space for inserting optical elements perpendicular to the optical axis without significantly increasing the overall axial length of the lens system, thereby improving adaptability while maintaining compactness.