Compact Photographing Lens with Moving Negative Group
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Solution Overview
Problem
Photographing lenses require further reduction in size and weight while maintaining good image forming performance, which existing designs have not adequately addressed.
Innovation Solution
A photographing lens configuration comprising a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group, where the second lens group moves along the optical axis upon focusing, with specific conditional expressions for lens parameters such as focal lengths, Abbe numbers, and air intervals to achieve compactness and light weight, and including a method for manufacturing this lens configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If the lens is designed to be compact and lightweight, then the size and weight are reduced, but image forming performance deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Abbe numbers of lens materials and the air intervals between lens groups. Specifically, it sets ν1bp−ν1bn≤32.0 for the first lens group and ν2n−2p≤30.0 for the second lens group, along with D1ab/D1≥0.40 and D2ab/D2≥0.40. These parameter constraints enable compact lens design while maintaining excellent aberration correction and image quality, resolving the contradiction between compactness and optical performance.
2Reliability
If the air interval between lens groups is increased, then aberration correction is improved, but the overall lens length increases
Solution Approach 1:
The patent resolves this contradiction by establishing specific parameter relationships: D1ab/D1≥0.40 and D2ab/D2≥0.40, where D1ab and D2ab are air intervals between lens groups, and D1 and D2 are their respective group lengths. This proportional relationship ensures sufficient air intervals for effective aberration correction while keeping the overall lens length compact through optimized group length ratios.
Solution Approach 2:
The patent applies local quality by making different lens groups have different structural characteristics. The first lens group has a positive overall power with specific Abbe number constraints (ν1bp−ν1bn≤32.0), while the second lens group has negative overall power with different constraints (ν2n−2p≤30.0). This localized optimization of each group's properties enables effective aberration correction within a compact overall structure.
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 enables a compact, lightweight lens with excellent image forming performance, effectively correcting aberrations and maintaining optical quality even at short focal lengths.
Implementation Method 1
a first lens group having positive refractive power; a second lens group having negative refractive power; and a third lens group having positive refractive power. The photographing lens is configured such that the second lens group moves along an optical axis upon focusing from an object at infinity to an object at a finite distance
Data Source
AI summary
Provided is a photographing lens (ML) including a first lens group (G1) having positive refractive power, a second lens group (G2) having negative refractive power, and a third lens group (G3) having positive refractive power, the photographing lens being configured such that the second lens group (G2) moves along the optical axis upon focusing from an object at infinity to an object at a finite distance. The first lens group (G1) includes a front lens group (G1a) and a rear lens group (G1b) having a longest air interval from the front lens group (G1a) in the first lens group (G1), and the second lens group (G2) includes a negative lens (L21) and a cemented lens in which a positive lens (22) and a negative lens (23) are cemented in order from the object.