Four-Group Zooming Lens for Wide Angle and Long Back Focus
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Solution Overview
Problem
Existing zooming optical systems face challenges in achieving a short focal length with a wide angle of view while maintaining a long back focus and effectively correcting aberrations, particularly for APS-C size image sensors, due to the difficulty in balancing diverging power and aberration correction.
Innovation Solution
A zooming optical system configuration comprising a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with negative refractive power, and a fourth lens group with positive refractive power, where each group moves along the optical axis, with specific focal length ratios and cemented lens configurations to balance power and correct aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a lens group with strong diverging power is disposed in front to achieve short focal length and wide angle of view, then the focal length is reduced and angle of view is widened, but aberration correction becomes difficult
Solution Approach 1:
The first lens group is divided into multiple lens elements including a negative lens closest to the object, a positive lens, and a cemented lens combination. This segmentation allows each element to contribute differently to the overall optical function, enabling strong diverging power while maintaining aberration correction capability through the coordinated action of individual elements with opposite signs of refractive power
Solution Approach 2:
Different regions of the optical system are assigned different functions: the negative lens closest to the object provides strong diverging power for wide angle of view, while the cemented lens combination with positive refractive power locally corrects aberrations in that specific region. This local quality differentiation resolves the contradiction between overall diverging power and local aberration correction
2Length of moving object
If the diverging power of the first lens group is increased to achieve short focal length, then the focal length is reduced, but the back focus becomes insufficient
Solution Approach 1:
The optical system uses an asymmetric four-group configuration (negative, positive, negative, positive) rather than a symmetric design. The first lens group with negative refractive power is positioned to provide diverging effect that extends the back focus distance, while the subsequent groups compensate to maintain short focal length. This asymmetric arrangement allows independent optimization of focal length and back focus parameters
Solution Approach 2:
The second and third lens groups act as intermediaries between the first lens group (which provides strong diverging power) and the imaging plane. These intermediate groups help extend the back focus distance by their optical power contributions, mediating the conflict between short focal length requirement and long back focus requirement
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 allows for a wide angle of view and long back focus while effectively correcting various aberrations, such as coma and spherical aberrations, across the zooming range, enhancing optical performance.
Implementation Method 1
a first lens group having negative refractive power... The first lens group has at least one cemented lens having positive refractive power
Implementation Method 2
Each of the first lens group, the second lens group, the third lens group, and the fourth lens group are configured to moves along a direction of an optical axis in zooming
Data Source
AI summary
A zooming optical system includes a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power, in that order from an object side. The first lens group has at least one cemented lens having positive refractive power. Each of the first lens group, the second lens group, the third lens group, and the fourth lens group are configured to move along a direction of an optical axis in zooming. Conditional expression (1) below is satisfied:−10.0<f2/f1<−2.0 (1),wheref1 is a focal length of the first lens group, andf2 is a focal length of the second lens group.