Inner Focus Lens System Compactness and Aberration Control

The lens system is divided into multiple lens units (first lens unit, second lens unit, third lens unit) with different refractive powers and movement characteristics. Each unit is optimized independently to contribute to overall aberration suppression while maintaining compactness. The most object-side lens unit is fixed during focusing, while the second lens unit moves along the optical axis, allowing precise control over optical path length and aberration characteristics.

The patent applies specific mathematical conditions to optimize the lens system parameters: BF/Y ≥ 1.7 and (L×FNo)/f ≥ 1.6, where BF is the back focal length, Y is the image height, L is the overall length, FNo is the F-number, and f is the focal length. By satisfying these inequalities, the system achieves compact size while maintaining high resolution and aberration suppression performance.

While the most object-side lens unit is fixed, the second lens unit is designed to move along the optical axis during focusing from infinity to close objects. This dynamic movement allows the system to compensate for image blur and aberrations that would otherwise result from a completely fixed lens configuration, maintaining high imaging quality across different focus distances.

The second lens unit acts as an intermediary between the fixed most object-side lens unit and the image sensor. By moving this intermediate lens unit along the optical axis, the system can adjust the optical path length and compensate for aberrations without requiring the entire lens system to be complex or the most object-side unit to move.