Rear Attachment Lens with Segmented Groups for Extended Focal Length

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Solution Overview

Problem

Existing rear attachment lenses for cameras fail to sufficiently increase the focal length of the whole lens system while ensuring a long back focal length and adequately correcting aberrations such as chromatic aberration, longitudinal chromatic aberration, spherical aberration, and astigmatism.

Innovation Solution

A rear attachment lens with a positive refractive power configuration, comprising a most object side lens with negative refractive power and a most image side lens with positive refractive power, optimized by specific refractive index and Abbe number conditions to ensure a long focal length and corrected aberrations, and a three-group lens configuration with cemented lenses to minimize aberrations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If existing rear attachment lens designs are used to increase focal length, then the focal length extension effect is achieved, but the back focal length is insufficient

Engineering Contradiction:

Improvefocal length of whole lens systemVSAvoidback focal length

Core Design Contradiction:

Length of moving objectVSLength of stationary object

Solution Approach 1:

The rear attachment lens is divided into multiple lens groups (first lens group with negative refractive power, second lens group with positive refractive power, and third lens group with positive refractive power). This segmentation allows each group to contribute differently to the overall optical performance, enabling the system to achieve both extended focal length and sufficient back focal length by coordinating the effects of individual groups.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different lens groups are assigned specific local optical characteristics: the first lens group provides negative refractive power to extend the focal length, while the second and third lens groups provide positive refractive power to ensure sufficient back focal length. This local differentiation of optical properties resolves the contradiction between focal length extension and back focal length requirements.

Inventive Principle:

Principle #3Local quality

2Length of moving object

If existing rear attachment lens designs are used, then focal length change is achieved, but aberration correction is insufficient

Engineering Contradiction:

Improvefocal length of whole lens systemVSAvoidaberration correction quality

Core Design Contradiction:

Length of moving objectVSManufacturing precision

Solution Approach 1:

The lens system is segmented into three distinct lens groups, each responsible for correcting specific types of aberrations. The first lens group corrects spherical aberration and coma, the second lens group corrects chromatic aberration, and the third lens group corrects astigmatism and field curvature. This segmented approach to aberration correction ensures high manufacturing precision and optical quality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite lens structures including cemented lenses combining different glass materials with complementary dispersion properties. By using composite material combinations with different Abbe numbers and refractive indices, the system achieves superior aberration correction across multiple wavelengths and optical conditions.

Inventive Principle:

Principle #40Composite materials

3Ease of manufacture

If a simple lens structure is used for rear attachment, then ease of manufacture is improved, but optical performance deteriorates

Engineering Contradiction:

Improvelens structure simplicityVSAvoidoptical performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The rear attachment lens is segmented into three functional groups that can be manufactured and tested independently before final assembly. This modular segmentation maintains ease of manufacture while achieving high optical performance through coordinated design of each group's refractive power and physical characteristics.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent optimizes multiple parameters including the refractive powers of individual lens groups, the Abbe numbers of lens materials, and the spacing between lens groups. By carefully controlling these parameters within specific ranges, the system achieves high optical performance while maintaining manufacturability through standardized design tolerances.

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

The solution effectively increases the focal length of the whole lens system, ensures a sufficient back focal length, and satisfactorily corrects various aberrations, resulting in high optical performance.

Implementation Method 1

a most object side lens which has a negative refractive power and is disposed to be closest to an object side, and a most image side lens which has a positive refractive power and is disposed to be closest to an image side

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS10838166B2Rear attachment lens and imaging apparatus

Publication Date: 2020.11.17 FUJIFILM CORP

AI summary

The rear attachment lens has a positive refractive power as a whole, and is attached to an image side of a main lens so as to change a focal length of the whole lens system after attachment to a focal length longer than a focal length of the main lens. The rear attachment lens includes a most object side lens that is a lens which has a negative refractive power and is disposed to be closest to an object side, and a most image side lens that is a lens which has a positive refractive power and is disposed to be closest to the image side.