Optical System Rear Group Cemented Lens Aberration Control
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Solution Overview
Problem
Optical systems for cameras face challenges in achieving optimal imaging performance due to issues with chromatic aberration, Petzval sum, curvature of field, and overall system size, particularly in maintaining appropriate back focus and total optical length ratios.
Innovation Solution
The optical system is configured with a first lens group, a stop, and a rear group that includes at least one cemented lens, with specific conditional expressions governing the back focus and total optical length ratios to correct aberrations and maintain image quality, allowing for downsizing while ensuring effective filter placement and reduced shading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the optical system uses a compact design with reduced total optical length, then the system size is reduced, but the back focus becomes insufficient and filter placement becomes difficult
Solution Approach 1:
The optical system is divided into a first lens group and a rear group with distinct functional responsibilities. The first lens group handles initial light convergence while the rear group corrects aberrations, allowing the back focus distance to be independently optimized for filter placement without proportionally increasing the entire system length.
Solution Approach 2:
Different regions of the optical system are optimized for different functions: the first lens group is designed for light gathering and initial focusing, while the rear group is specifically optimized for aberration correction. This local optimization allows the back focus region to maintain adequate length for filter placement while the overall system remains compact.
2Reliability
If the optical system uses cemented lenses to correct chromatic aberration, then imaging performance is improved, but the Petzval sum becomes difficult to control and curvature of field increases
Solution Approach 1:
The patent carefully selects and adjusts optical parameters including refractive indices, Abbe numbers, and focal lengths of individual lenses within the rear group. By changing these parameters, the system achieves effective chromatic aberration correction through cemented lenses while simultaneously controlling the Petzval sum to minimize curvature of field.
Solution Approach 2:
The rear group employs composite lens structures with cemented elements having different refractive indices and dispersion properties. This composite approach allows the system to correct chromatic aberration while the specific combination of materials and designs keeps the Petzval sum within acceptable ranges to reduce curvature of field.
3Adaptability or versatility
If the optical system increases the ratio of back focus to maximum image height, then filter placement is enabled, but the total optical length increases and system compactness is reduced
Solution Approach 1:
The optical system is divided into a first lens group and a rear group with distinct functional responsibilities. The first lens group handles initial light convergence while the rear group corrects aberrations, allowing the back focus distance to be independently optimized for filter placement without proportionally increasing the entire system length.
Solution Approach 2:
The rear group serves multiple functions: it corrects chromatic aberration, controls the Petzval sum, reduces curvature of field, and provides the necessary back focus distance for filter placement. This multi-functionality allows adequate filter placement capability while keeping the total optical length compact.
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 effectively corrects chromatic aberration, maintains the Petzval sum, and reduces aberrations, enabling a compact optical system with improved imaging performance by adhering to specific conditional expressions for back focus and total optical length ratios.
Implementation Method 1
the rear group includes at least one cemented lens; all of the following conditional expressions are satisfied: 0.35<Bf/y≤0.55
Implementation Method 2
maintains the Petzval sum, and reduces aberrations
Implementation Method 3
the optical system has an air gap between a lens disposed closest to an image-plane side of one or more lenses included in the first lens group and the stop
Data Source
AI summary
An optical system is configured to include, in order from an object side, a first lens group, a stop, and a rear group including at least one cemented lens, and to satisfy all of the following conditional expressions:0.35<Bf/y<0.701.35<TL/y<1.85where Bf is a back focus in air-equivalent length, and y is a maximum image height.Further, an optical system is configured to include, in order from an object side, a first lens group, a stop, and a rear group having an air gap between a lens disposed closest to an image-plane side of one or more lenses included in the first lens group and the stop, and to satisfy the following conditional expression:1.35<TL/y<1.85where TL is the distance from a lens surface closest to the object side to an image plane at focusing on an object at infinity, and y is a maximum image height.