Telecentric Optical System for Accurate BRDF Imaging
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Solution Overview
Problem
Existing optical systems for measuring bidirectional reflectance distribution function (BRDF) struggle to acquire two-dimensional images that resemble visual observations, due to misalignment of the aperture stop and intermediate image position, leading to inclined observation angles and deviations from visual appearance.
Innovation Solution
The optical system includes a first optical system with a relay configuration forming an intermediate image, and a second optical system sharing a common lens group, with the aperture stop positioned to satisfy the conditional expression Δp/f1 between -1.0 and 3.0, allowing for a telecentric configuration and accurate two-dimensional imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the aperture stop is located far away from the intermediate image position in the optical system for acquiring a two-dimensional image, then the optical system can share lenses with the BRDF measurement optical system, but the observation angle is greatly inclined in the peripheral portion of the measurement area, causing the captured image to deviate from visual observation
Solution Approach 1:
The patent applies parameter changes by precisely adjusting the aperture stop position relative to the intermediate image position. By setting the distance between the aperture stop and intermediate image position to a specific range (0.5-2.0 times the focal length of the objective lens), the system transforms from a non-telecentric configuration to an object-side telecentric configuration. This parameter adjustment corrects the observation angle inclination while maintaining the shared lens structure, thereby resolving the contradiction between device complexity and image fidelity.
2Measurement precision
If a goniophotometer is used to measure BRDF, then measurement of bidirectional reflectance distribution function is achieved, but the measurement takes time, the device is large, and discrete illumination and reception angles are measured
Solution Approach 1:
The patent replaces the mechanical scanning system of traditional goniophotometers with a stationary optical system. Instead of mechanically moving illumination and detection units to measure discrete angles, the invention uses a fixed optical system with a specific aperture stop position that enables continuous angle measurement. The object-side telecentric configuration allows all reflection angles to be captured simultaneously without mechanical movement, dramatically reducing measurement time while maintaining BRDF measurement precision.
Solution Approach 2:
The patent achieves multi-functionality by designing an optical system that simultaneously performs BRDF measurement and two-dimensional image acquisition. The shared lens structure (objective lens and tube lens are common to both functions) allows the system to measure optical characteristics and capture images without requiring separate dedicated devices, thereby improving productivity without sacrificing measurement precision.
3Measurement precision
If the aperture stop is positioned to create an object side telecentric optical system, then the observation angle is corrected and the image resembles visual observation, but the aperture stop must be precisely positioned near the intermediate image position
Solution Approach 1:
The patent defines a specific parameter range for the aperture stop position (0.5-2.0 times the focal length of the objective lens from the intermediate image position) that ensures object-side telecentric configuration. By establishing this quantitative parameter range, the invention makes the positioning requirement more manageable and less sensitive to small deviations, thereby improving ease of manufacture while maintaining image fidelity.
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 the acquisition of two-dimensional images that closely resemble visual observations, while simultaneously measuring optical characteristics, thereby addressing the limitations of existing systems in terms of time, size, and image fidelity.
Implementation Method 1
a first lens group having positive power, a second lens group having positive power... the first optical system being a relay optical system that forms an intermediate image between the first lens group and the second lens group
Implementation Method 2
the aperture stop being arranged in the second lens group such that an entrance pupil of the aperture stop is on an object side of the first lens group
Implementation Method 3
a first imaging element, and an illumination light source... a second imaging element, the second imaging element being arranged at a position conjugate with the measurement target
Data Source
AI summary
Provided are an optical system for measuring optical characteristics and a device for measuring optical characteristics capable of acquiring a two-dimensional image close to visual observation in addition to measurement of optical characteristics of a measurement target. The optical system for measuring optical characteristics includes a first optical system (11) that captures an infinite conjugate image and a second optical system (12) that captures a conjugate image of a measurement target. The first optical system (11) and the second optical system (12) sharing a first lens group (G1) are arranged on two optical axes separated by an optical element (5) that deflects an optical axis, respectively, and are configured as one measuring optical system. Furthermore, an aperture stop of the second optical system (12) is arranged in the vicinity of an intermediate image. When a distance in an optical axis direction from an image side paraxial focal point of the first lens group (G1) to the aperture stop is represented by Δp, and a focal distance of the first lens group is represented by f1, Δp/f1 satisfies −1.0<Δp/f1<3.0.