Image Pickup Lens System Compact Design Exit Pupil Control
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Solution Overview
Problem
The challenge is to create a compact image pickup lens system for digital cameras that maintains good optical performance while keeping the exit pupil position far from the image surface, as miniaturization efforts often compromise image quality and increase system length.
Innovation Solution
The system employs a four-lens configuration with a positive first lens, an aperture stop, a negative third lens with a concave surface facing the image surface, and a positive fourth lens, satisfying specific conditional expressions to balance optical performance and compactness, including the condition 0.05 < T3/f < 0.5, where T3 is the axial thickness of the third lens and f is the focal length of the whole system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of the image pickup lens system is decreased, then the compactness is improved, but the exit pupil position becomes near to the image surface causing off-axis luminous flux to be obliquely incident
Solution Approach 1:
The patent applies parameter changes by carefully controlling the axial thickness of the third lens (T3) relative to the focal length (f) within the range 0.05 < T3/f < 0.5, and positioning the aperture stop at a specific distance from the third lens. These parameter adjustments enable the exit pupil to be positioned far from the image surface while maintaining a compact overall lens size, thus resolving the contradiction between compactness and focusing performance.
2Reliability
If the exit pupil position is kept far away from the image surface, then the focusing performance is improved, but the size of the image pickup lens system increases
Solution Approach 1:
The patent resolves this contradiction by optimizing specific parameters: the axial thickness of the third lens (T3/f between 0.05 and 0.5) and the distance from the third lens to the aperture stop. These parameter changes enable the system to maintain a compact size while positioning the exit pupil far from the image surface, ensuring both compactness and focusing performance.
Solution Approach 2:
The patent employs a composite lens structure with four lenses having different optical powers (positive, positive, negative, positive) and specific configurations. This composite structure allows the system to achieve both compactness and proper exit pupil positioning by distributing optical functions across multiple elements with carefully selected properties.
3Reliability
If a four-lens configuration with the first lens being negative is used, then the optical performance is improved, but the total length of the lens is increased
Solution Approach 1:
The patent applies inversion by reversing the conventional lens configuration: instead of starting with a negative first lens, it uses a positive first lens followed by a negative third lens. This inverted arrangement, combined with positioning the aperture stop after the third lens, enables both compact total length and good optical performance by redistributing the optical power sequence.
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 achieves high optical performance, maintains an appropriate exit pupil position, and ensures compactness, contributing to cost reduction and miniaturization in digital input equipment such as cameras.
Implementation Method 1
an image pickup lens system includes, from an object side, a positive first lens, an aperture stop, a positive second lens, a negative third lens whose concave surface is faced toward an image surface side, and a positive fourth lens
Data Source
AI summary
An image pickup lens system has a four-lens configuration which forms an image on a solid-state image pickup device. The image pickup lens system includes, from an object side, a positive first lens, an aperture stop, a positive second lens, a negative third lens whose concave surface is faced toward an image surface side, and a positive fourth lens in the order from an object side. A ratio of an axial lens thickness of the third lens to a focal length of the whole system is optimally set. Therefore, an exit pupil position can be kept far away from the image surface while the image pickup lens system has good optical performance and a compact size.