Objective Lens Diffractive Element Long Working Distance
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Solution Overview
Problem
Objective lenses with highly corrected chromatic aberration have insufficient working distance for industrial use and suffer from large undulations in spherical aberration and coma, particularly when trying to maintain a long working distance.
Innovation Solution
An objective lens design comprising a first lens group with positive refractive power, a second lens group with positive refractive power, a diffractive optical element, and a third lens group with negative refractive power, where the diffractive optical element is positioned near the principal ray's crossing point between the second and third lens groups, and specific conditional expressions are satisfied to optimize focal lengths and refractive indices, ensuring a long working distance and improved aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a long working distance is secured by increasing the object side focal length and disposing a negative lens group to the image side, then the working distance is improved, but chromatic aberration becomes worse
Solution Approach 1:
A diffractive optical element is introduced as an intermediary component between the second and third lens groups. This element provides negative dispersion to counterbalance the positive dispersion from the lens groups, enabling chromatic aberration correction while maintaining the long working distance achieved through the extended focal length design.
Solution Approach 2:
The objective lens employs a composite optical system combining refractive lens groups with a diffractive optical element. This composite structure integrates both refractive and diffractive optical functions, allowing simultaneous achievement of long working distance and chromatic aberration correction through the synergistic interaction of different optical mechanisms.
2Manufacturing precision
If chromatic aberration is highly corrected using existing designs, then chromatic aberration correction is improved, but working distance becomes insufficient for industrial use
Solution Approach 1:
The invention optimizes specific parameters including the focal length of the third lens group (|f3/fa| between 1.0-5.0), the position of the diffractive optical element, and the dispersion characteristics of lens materials. These parameter adjustments enable the system to achieve both high chromatic aberration correction and sufficient working distance for industrial applications.
3Length of moving object
If a negative lens group with strong refractive power is disposed to the image side to achieve long working distance, then working distance is improved, but spherical aberration and coma exhibit large undulation
Solution Approach 1:
The third lens group is divided into multiple cemented lenses with different refractive powers and dispersion characteristics. This segmentation allows independent optimization of each sub-component to control spherical aberration and coma while collectively providing the necessary negative refractive power for long working distance.
Solution Approach 2:
Different regions of the third lens group are designed with locally optimized properties - the first lens has positive refractive power with specific dispersion characteristics, while the second lens has negative refractive power. This local quality differentiation enables precise control of off-axis aberrations like coma and spherical aberration throughout the field of view.
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 design achieves a long working distance with highly corrected chromatic aberration, balancing longitudinal and lateral chromatic aberration corrections while minimizing spherical aberration and coma, thereby enhancing the optical performance for industrial applications.
Implementation Method 1
a diffractive optical element having a diffractive optical surface
Implementation Method 2
The first lens group includes at least one cemented lens and the most object side surface thereof forms a concave surface facing the object side. The second lens group includes at least one cemented lens. The third lens group includes at least one cemented negative lens.
Data Source
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AI summary
An objective lens OL includes, in order from an object, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, a diffractive optical element GD forming a diffractive optical surface D thereon, and a third lens group G3 having negative refractive power. The first lens group G1 includes at least one cemented lens and the most object side surface thereof forms a concave surface facing the object. The second lens group G2 includes at least one cemented ens. The third lens group G3 includes at least one cemented negative lens. In the objective lens OL, a principal ray crosses an optical axis between the second lens group G2 and the third lens group G3, and in the diffractive optical element GD, the diffractive optical surface D is disposed in the vicinity of the position where the principal ray crosses the optical axis.