Infrared Lens Unit with Uncoated Edge for Tilt Error Suppression
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Solution Overview
Problem
Existing finite-type spectral characteristic measurement devices face significant challenges in suppressing tilt errors, particularly in the infrared region (7 μm to 14 μm), due to the inherent molecular vibration absorption, which affects the optical properties.
Innovation Solution
A lens unit design that includes at least one lens with a coating film, a lens barrel with a specific hole configuration, and ring parts to securely position the lenses on the optical axis, with a non-attachment region on the circumferential edge parts where the coating film is not attached, to prevent tilt errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating film is formed on the lens surface to improve optical properties in the infrared region, then the transmittance and reduction of reflection loss are improved, but the lens becomes more prone to tilt errors when mounted in the lens barrel
Solution Approach 1:
The lens surface is segmented into two functional zones: an optical effective area with coating film for optimal light transmission, and a circumferential edge region without coating film for precise mechanical mounting. This segmentation allows the coating film to be applied selectively only where optical performance is critical, while the uncoated edge portion provides a reliable mounting surface that prevents tilt errors during assembly into the lens barrel.
Solution Approach 2:
Different regions of the lens surface are given different properties: the central optical area receives the coating film to enhance infrared transmittance and reduce reflection, while the peripheral edge area remains uncoated to ensure accurate mechanical positioning and minimize tilt errors. This local differentiation of surface quality resolves the contradiction between optical performance and mounting precision.
2Volume of moving object
If the lens is mounted at a short distance from the measurement target (finite-type configuration), then the device compactness is improved, but the tilt error significantly affects optical properties
Solution Approach 1:
The circumferential edge region is prepared in advance by excluding the coating film during the coating process, creating a pre-designed mounting zone. This preliminary preparation ensures that when the lens is mounted in the lens barrel at short distances from the measurement target, the uncoated edge provides optimal contact surfaces that inherently resist tilt errors, thereby maintaining optical property stability despite the compact finite-type configuration.
3Reliability
If the coating film is applied over the entire lens surface to maximize optical coverage, then the reflection reduction is improved, but the mounting precision and tilt error suppression are degraded
Solution Approach 1:
The lens surface coating application is segmented into two distinct zones: the optical effective area where the coating film is applied to maximize reflection reduction and improve transmittance, and the circumferential edge area where the coating film is deliberately excluded to provide optimal mounting surfaces. This selective segmentation resolves the contradiction by applying the coating only where it provides optical benefit while preserving mounting precision at the edges.
Solution Approach 2:
The lens surface exhibits local quality differentiation through selective coating application. The central and intermediate regions possess the coating film's reflective and transmissive properties, while the peripheral circumferential edge maintains the substrate's original surface characteristics for optimal mechanical contact and positioning, thereby preventing tilt errors during mounting.
Data Source
AI summary
Provided is a lens unit that is for an infrared region and that allows occurrence of a tilt error to be easily suppressed. A lens unit (4) is a lens unit which is used for an infrared region that includes at least any one of wavelengths in a range of 7 μm to 14 μm, and includes: at least one lens (1, 2, 3) that has a surface on which a coating film is formed; a lens barrel (6) that has a hole (61, 62, 63) in which the at least one lens is fitted; a ring part (65, 66, 67) that is a member which is in contact with a circumferential edge part (1c, 2c, 3c) of the at least one lens and which is for causing the at least one lens fitted in the hole to be located at a given position on an optical axis of the lens barrel (6) or fixing, at a given position on the optical axis of the lens barrel, the at least one lens fitted in the hole. The circumferential edge part of the at least one lens has, on a portion which is in contact with at least any one of the lens barrel and the ring part, a region in which the coating film is not attached.