Athermalized Imaging Lens with Segmented Optical Groups
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Solution Overview
Problem
Current optical lenses used in aerial mapping suffer from significant distortion, lack of telecentricity, uncorrected chromatic aberrations, and thermal instability, making them unsuitable for high-resolution airborne photography and precise mapping applications.
Innovation Solution
A compact, low distortion lens design with a full field of view of 60° and near-telecentricity, apochromatic over 450 nm-650 nm wavelength range, and athermalized over -15°C to +40°C temperature range, featuring three groups of optical elements with specific configurations to correct for spherical aberration, chromatic aberrations, and field curvature, while minimizing light loss and maintaining high resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical lenses are used for aerial mapping, then the lens can capture images, but the lens produces significant distortion and lacks telecentricity
Solution Approach 1:
The lens is divided into three distinct optical groups (first optical group with positive power, second optical group with negative power, and third optical group with positive power), each performing specific correction functions. This segmentation allows independent optimization of distortion correction, telecentricity, and chromatic aberration correction without requiring complete redesign of the entire lens system.
Solution Approach 2:
The patent employs a reverse telephoto configuration where the optical groups are arranged in an inverted sequence compared to conventional lenses, with the negative power group positioned between two positive power groups. This inversion enables simultaneous achievement of wide field of view, telecentricity, and low distortion that cannot be obtained with traditional lens arrangements.
2Reliability
If the lens operates over a wide temperature range, then the lens must be athermalized, but this increases design complexity
Solution Approach 1:
The patent achieves athermalization by carefully selecting optical materials with specific thermal expansion coefficients and refractive index temperature dependencies. The design parameters of the optical groups are optimized to compensate for thermal effects, allowing the lens to maintain focus and optical performance across the temperature range of -15°C to +40°C without mechanical adjustment mechanisms.
Solution Approach 2:
The lens utilizes composite optical systems combining multiple glass types with different thermal properties. By integrating materials with complementary thermal characteristics in the three optical groups, the design achieves natural athermalization where the thermal expansion and refractive index changes of one material compensate for those of another, eliminating the need for active thermal control.
3Measurement precision
If the lens corrects for chromatic aberrations, then image quality improves, but the lens design becomes more complex
Solution Approach 1:
Chromatic aberration correction is distributed across the three optical groups, with each group containing optical elements made from specific glass types selected for their dispersion properties. The first and third groups use positive power elements that converge light, while the second group uses negative power elements that diverge light, creating a balanced correction system that addresses both primary and secondary spectrum without requiring excessive optical elements.
Solution Approach 2:
Different regions of the lens system are assigned different glass materials with specific dispersion characteristics tailored to their local function. The optical groups are configured with materials that have varying Abbe numbers and partial dispersion ratios, allowing targeted correction of chromatic aberrations in specific wavelength ranges while maintaining overall image quality across the visible spectrum.
4Measurement precision
If the lens achieves near-telecentricity, then measurement accuracy improves, but the lens length increases
Solution Approach 1:
The reverse telephoto configuration inverts the traditional lens arrangement, placing the aperture stop in a position that enables near-telecentric operation with a compact overall length. The specific sequencing of positive-negative-positive optical groups creates parallel chief rays at the image plane without requiring excessive back focal distance, achieving telecentricity in a space-efficient manner suitable for aerial mapping applications.
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 lens achieves less than 0.6% distortion, high-quality performance across a wide field of view, and maintains image quality without the need for thermal adjustments, ensuring reliable performance in varying temperatures and altitudes.
Implementation Method 1
The lens includes a first optical group including a plurality of optical elements, a second optical group including a plurality of optical elements, an aperture located within the second optical group, and a third optical group including a plurality of optical elements
Implementation Method 2
Optical distortion is a function of the viewing angle. The distortion of lenses used in aerial mapping should be less than 0.5%. Such lenses should be able to operate at different altitudes, from sea level and up to 30000 feet.
Implementation Method 3
When the chromatic aberration is not corrected, each wavelength is focused at a different point along the optical axis. If the optical system is achromatized over a given bandwith, the outer wavelengths of the bandwidth have a common focus.
Implementation Method 4
As ambient temperature conditions change, the shapes and positions of optical elements in a lens will change, and the focal length and position of an image formed by the lens will change as well.
Data Source
AI summary
A compact, lens suitable for airborne photography and mapping has distortion less than 0.6% and is athermal from −15° C. to +40° C. The lens is near-telecentric to less than 11°, apochromatic over the wavelength range 450 nm-650 nm, and has a full field of view of 60° (high quality field over 53°). The lens can be secondary color corrected. In embodiments, the focal length is 101 mm and the back working distance is more than 10 mm. Embodiments have a focal plane diameter of 104 mm and are compatible for use with a CMOS 1.8 gigapixel multiple FPA. In embodiments, the lens comprises three groups of optical elements, with an aperture located within the second optical group. In some embodiments the first group includes two elements, the second group includes six or seven elements, and the third group include three elements. In embodiments the lens (without window) is less than 180 mm long.