Imaging Optical System with Moving Rear Lens for Autofocus

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Solution Overview

Problem

Existing large-aperture imaging optical systems face challenges in maintaining sharp image formation across the entire focus range, including infinity to close-range, while achieving high-speed autofocus, due to significant aberrations and weight issues with focus lenses.

Innovation Solution

The proposed imaging optical system includes a front group, aperture stop, and rear group with specific lens configurations, where the single lens Fn moves along the optical axis during focusing, allowing for high-speed autofocus without moving the front or rear groups, and satisfies specific focal length ratios to minimize aberrations and weight.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a large-aperture imaging optical system uses multiple lens groups for focusing, then the focusing range from infinity to close-range is improved, but the device complexity and weight increase

Engineering Contradiction:

Improveimage sharpnessVSAvoidlens group configuration

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The optical system is divided into three main segments: front group (positive power), aperture stop, and rear group (negative power). This segmentation allows each group to have optimized functions - the front group for light gathering and the rear group for focus adjustment, reducing overall complexity while maintaining image quality

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of moving the front group toward the object during focusing, the rear group with negative power is moved toward the image plane. This inverted approach achieves the same focusing effect with reduced complexity and weight, as the rear group can be made lighter due to its negative power requirement

Inventive Principle:

Principle #13The other way round (Inversion)

2Manufacturing precision

If focus lenses are made heavier to maintain image quality across focus ranges, then image sharpness is improved, but autofocus speed decreases

Engineering Contradiction:

Improveimage sharpnessVSAvoidautofocus speed

Core Design Contradiction:

Manufacturing precisionVSSpeed

Solution Approach 1:

The focusing function is separated into a dedicated rear group that moves independently. This segmentation allows the focus lens to be optimized for speed (lighter weight) while the front group maintains image quality through its fixed positive power configuration

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The power distribution parameters are optimized such that the rear group has negative power, allowing it to be lighter and move faster for autofocus, while the front group has positive power to maintain image sharpness. The focal length ratio fG1/fG2 is specifically controlled to balance these requirements

Inventive Principle:

Principle #35Parameter changes

3Illumination intensity

If the aperture stop is positioned differently in the optical system, then light gathering ability is improved, but aberration control worsens

Engineering Contradiction:

Improvelight gathering abilityVSAvoidaberrations

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

The aperture stop is positioned as an intermediary element between the front positive group and rear negative group. This intermediate positioning allows it to control the cone of light effectively for light gathering while the surrounding lens groups correct the resulting aberrations

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The aperture stop diameter and position are optimized as parameters to balance light gathering ability with aberration control. The F-number and aperture stop location are specifically tuned to work with the front and rear group configurations

Inventive Principle:

Principle #35Parameter changes

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 sharp image formation across the entire focus range with high-speed autofocus, reducing aberrations and maintaining performance from infinity to close-range, while also minimizing the weight of focus lenses.

Implementation Method 1

a single lens Fn arranged adjacent to the aperture stop and having negative power... While the imaging optical system is focusing to make a transition from an infinity in-focus state to a close-object in-focus state, neither the front group nor the rear group moves but the single lens Fn moves along an optical axis toward the image

Methodology Applied

Scientific EffectLens focusing: Lens

Data Source

PatentUS12061376B2Imaging optical system, and image capture device and camera system using the imaging optical system

Publication Date: 2024.08.13 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

An imaging optical system includes: a front group having positive power; an aperture stop; a single lens Fn arranged adjacent to the aperture stop and having negative power; and a rear group having power. The front group includes: a first lens having positive power; a second lens having negative power; and a lens LG1R having positive power. The rear group includes a lens LGnR having negative power and located closest to the image. While focusing to make a transition from an infinity in-focus state to a close-object in-focus state, neither the front group nor the rear group moves but the single lens Fn moves along an optical axis toward the image. The imaging optical system satisfies the inequality: 0.38<fLG1R/fG1<1.75, where fG1 is a focal length of the front group and fLG1R is a focal length of the lens LG1R.