Four-Group Zoom Lens Focusing Mechanism
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Solution Overview
Problem
Existing zoom lenses for interchangeable-lens-type digital cameras face challenges in achieving compactness while maintaining excellent imaging performance and high-speed, smooth focusing suitable for motion-picture imaging, due to large actuators and vibration/noise issues associated with heavy lens groups and complex lens configurations.
Innovation Solution
A zoom lens configuration with a first lens group having negative power, a second lens group having positive power, a third lens group having negative power, and a fourth lens group having positive power, where the first lens group moves along the optical axis to decrease its distance with the second lens group, and the second, third, and fourth lens groups move towards the object side for focusing, satisfying specific conditional expressions to optimize focal length and travel ratios, and incorporating aspheric surfaces for aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a two-group zoom lens is used with a large first lens group for focusing, then focusing capability is achieved, but the actuator becomes large and heavy, preventing size reduction and producing vibration and noise
Solution Approach 1:
The lens system is divided into four groups with specific focusing functions assigned to the third lens group rather than moving the entire first lens group. This segmentation allows the actuator to only move the lighter third lens group, reducing actuator weight and size while maintaining focusing capability.
Solution Approach 2:
Instead of moving the first lens group for focusing as in conventional designs, the invention inverts the approach by making the third lens group the focusing element. This inversion allows for a more compact actuator and reduces the moving mass during focusing operations.
2Volume of moving object
If a three-group zoom lens with a third lens group used as focusing lens group is used, then compactness is improved, but the third lens group becomes large and heavy in interchangeable lenses with large imaging devices
Solution Approach 1:
The third lens group is designed with specific optical characteristics (negative power, appropriate focal length) tailored to its focusing function. By optimizing its local optical properties and making it a separate movable unit, the design achieves compactness without excessive weight, as only this specific group needs to be moved for focusing.
3Volume of moving object
If a zoom lens with a third lens group having too small longitudinal magnification is used, then compactness is achieved, but a long focusing stroke is required, increasing actuator size and total lens length
Solution Approach 1:
The focal length of the third lens group is specifically optimized to satisfy the conditional expression -2.0 < f3/√(fw×ft) < -0.5. This parameter optimization ensures appropriate longitudinal magnification that shortens the focusing stroke while maintaining compact lens size, preventing the need for excessively long actuators.
4Volume of moving object
If the fourth lens group is positioned close to the image plane at telescopic end, then compactness is improved, but high-height light rays incident on the fourth lens group result in large lens diameter, interfering with the mount
Solution Approach 1:
The fourth lens group is positioned in the paraxial region (close to the optical axis) rather than at the periphery. This dimensional repositioning allows the lens to work with high-height light rays without requiring a large lens diameter, as the rays pass through the lens closer to the optical axis where the mount interference is minimized.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables compact size reduction, improved focusing precision, and effective aberration correction, ensuring high-quality imaging and smooth focusing performance for motion-picture applications.
Implementation Method 1
incorporating aspheric surfaces for aberration correction
Data Source
AI summary
A zoom lens includes: first, second, third and fourth lens groups having negative power, positive power, negative power and positive power, respectively, and sequentially arranged from an object side toward an image side. When the magnification at a wide angle side is changed to the magnification at a telescopic side, the first lens group is so moved along an optical axis that the distance between the first lens group and the second lens group decreases, and the second third and fourth lens groups are moved from the image side toward the object side, the third lens group is moved along the optical axis for focusing, and the zoom lens satisfies the following conditional expression (1)−2.0<f3/√(fw×ft)<−0.3 (1)where f3, fw and ft represent the focal lengths of the third lens group, the entire lens system at the wide angle end, and the entire lens system at the telescopic end, respectively.