A novel in situ calibration of object distance of an imaging lens based on optical refraction and two-dimensional DIC. (September 2019)

• Record Type: Journal Article
• Authors: Zhu, Feipeng; Lu, Runzhi; Bai, Pengxiang; Lei, Dong
• Is Part Of: Optics and lasers in engineering. Volume 120(2019)
• Page Start: 110
• Page End: 117
• Publication Date: 2019-09
• Subjects: In situ calibration -- Object distance -- Digital image correlation -- Strain field -- Refraction -- Displacement field; Lasers in engineering -- Periodicals; Optical measurements -- Periodicals; Optics -- Periodicals; Lasers en ingénierie -- Périodiques; Mesures optiques -- Périodiques; Optique -- Périodiques; 621.36605
• DOI: 10.1016/j.optlaseng.2019.03.023
• Languages: English
• ISSNs: 0143-8166

Abstract

Highlights: A novel calibration is proposed to determine the object distance of an imaging lens. An image displacement with ideal linear distribution is produced by refraction in a real experiment. The proposed calibration show good agreements with those obtained by conventional calibration. The proposed calibration proves to be an easy-to-implement in situ calibration for the object distance of an imaging lens. Abstract: The strain results of two-dimensional digital image correlation (2D-DIC) are known to be markedly affected by out-of-plane motion in practical measurements. To correct strain results, it is necessary to measure the object distance of the camera imaging lens. Due to the difficulty of conventional calibration using a translation stage, a novel in situ calibration based on optical refraction is proposed herein to determine the object distance. In our calibration, recorded images show a radial outward displacement field when a glass plate is placed in front of a planar specimen. This study presents a formula derivation of the displacement and strain distributions theoretical model. Based on the strain model and the calculated strain fields obtained using a 2D-DIC algorithm, the object distance can be obtained with a high measurement accuracy. Experiments were conducted to verify the validity and reliability of the proposed calibration. Comparison results between a conventional translation calibration and the proposed calibration indicate that the proposed calibration can reach a measurement accuracy of 0.19% (1.2 mm in this paper). This experiment demonstrates that the proposed calibration is an easily implemented method for the in situ computation of the object distance of an imaging lens.