• Journal of Korean Ophthalmic Optics Society
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• v.20 no.3
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• pp.263-276
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• 2015

Purpose: The current study aimed to evaluate the reliability for the combined refractive power when a spherical lens and a cylindrical lens were overlapped in a trial frame. Methods: The refractive powers, central thickness and peripheral thickness of spherical trial lenses and cylindrical lenses with negative power were measured. The combined refractive power of the spherical and cylindrical lenses was measured by auto lens meter. Measurement was repeated by changing the insertion order, and their results were further compared with the calculated combined refractive power. Results: There was no correlation between the variation of central and peripheral thickness in trial lenses and that of the lens power. Among 79 trial lenses, 3 trial lenses wasn't met the international standard. The refractive power calculated by Gullstrand's formula that could compensate vertex distance had smaller difference with the estimated power when compared with that calculated by thin lens formula however, it was significantly different from the estimated power. The refractive powers were generally apparent regardless of the insertion order of a spherical lens and a cylindrical lens: thin lens formula > actual measurements > Gullstrand's formula. The error was only found in cylindrical power calculated by Gullstrand's formula when inserted a spherical lens inside and a cylindrical lens outside however, the error was found in both of cylindrical and spherical powers calculated by Gullstrand's formula when inserted as a opposite order. By comparing actual measurements of equivalent spherical power, the accuracy was higher and the possibility of over-correction was lower when inserted a spherical lens inside and a cylindrical lens outside. Conclusions: From the results, those were revealed that the combined refractive power is influenced by the factors other than the vertex distance and the refractive power varies in accordance with the insertion order of a spherical lens and a cylindrical lens. Thus, it can be suggested that the establishment of standard for these is neccesaty.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.1
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• pp.157-164
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• 2017

In this research, the overlapped illumination model was used for designing a freeform LED lens with a uniform illuminance distribution on its illuminating plane, and their performances and tolerances were compared. And, the illuminations on a illumination plane was measures for change with average illuminance and illuminance uniformity. As a result of the tolerance analysis about z-axis direction change, thickness change in lens and tilt change of light emission and characteristic change in LED source, overlapped model and divergent illumination model are similar to the performance about Z-axis direction change of light emission in LED source. but the uniformity illumination value in this overlapped model is more remarkably value than it in divergent illumination model about thickness change in LED lens. Also, even though the lens based on a divergent illumination model showed good performance compare to the lens based on an overlapped illumination model, the latter was less the deviation to variation of LED beam radiation ability.

• Korean Journal of Optics and Photonics
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• v.33 no.6
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• pp.317-323
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• 2022

In this investigation, we describe a chromatic confocal sensor based on a geometric phase lens for measuring the thicknesses of transparent plates. In order to design a compact sensor, a geometric phase lens, which has diffractive and polarizing characteristics, is used as a device to generate chromatic aberration, and a fiber optic module is adopted. The systematic error of the sensor is reduced with wavelength peak detection by Gaussian curve fitting and the common error compensation obtained by the repeatedly consecutive experimental results. An approach to calculate the plate thickness is derived and verified with sapphire and BK7 plates. Because of the simple and compact design of the proposed sensor with rapid measurement capability, it is expected to be widely used in thickness measurements of transparent plates as an alternative to traditional approaches.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.6
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• pp.239-242
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• 2016

In this paper, we proposed the dual curved lens of concave type. HDPE (High Density Polyethylene) used to fabricate the dual curved lens. The dual curved lens consisted of two concave structures. Role of two concave structures is to beam uniform and expansion. A small concave structure has the greater curvature than big concave structure. The dual curved lens will apply to millimeter imaging system. We measured the dual curved lens performance using 250 GHz VDI source. And we simulated the dual curved lens using ZEMAX. Fabricated lens have a good performance for beam uniform and expansion.

• The Optical Journal
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• s.97
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• pp.58-61
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• 2005

복굴절이란 하나의 매질로부터 다른 매질로 진입하는 파동이 그 경계면에서 나가는 방향을 바꾸는 현상으로 등방성 매질에서 이방성 매질로 나아갈 때는 경계면에서 굴절파가 두 개로 나뉘어 굴절하게 되는 것을 말한다. 휴대폰용 카메라모듈 렌즈의 사출성형공정에서 발생하는 렌즈 내의 잔류응력에 의한 복굴절률은 사출공정에서의 렌즈불량 발생의 원인이 되며, 잔류응력은 또한 사출성형 이후에 완화되어 렌즈의 외관 치수의 변형을 가져오게 된다. 그러나 플라스틱류를 사용하는 정밀가공 생산 공정 등 실생활에서는 제품의 제조에 있어서 복굴절은 광학적 특성을 결정하는 가장 중요한 요소 중의 하나로서 성형시 복굴절을 최소화할 필요가 있다. 이를 어느 정도 달성했는가의 수준에 따라 플라스틱 정밀 성형 제품의 등급이 결정되는 중요한 측정요소이다.

• Journal of Korean Ophthalmic Optics Society
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• v.7 no.2
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• pp.1-11
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• 2002

A mathematical model is proposed to analyze the force; acting on the hard contact lens fitted on the cornea. The model incorporates the nonlinear equations and their numerical solution program, based on the formulations of surface tension force arising from the capillary action in the tear-film layer between the lens and cornea. The model simulates how the adhesion between lens and cornea varies according to the base curves and diameters of the lenses. When the spherical lens is fitted on the spherical cornea it is to rotate downward due to the weight of lens itself until it reaches an equilibrium position along the cornea where the counter(upward) moment caused by net force between the upper and lower portion of the periphery of lens. It is found that both the adhesion and displacement of lens along the cornea, where the gravity of lens balances the capillary-induced upward force, increases rapidly as the base curve of lens increases, i.e., as the lens gets flatter, while the increase in the diameter of lenses has resulted in the less increase in the rotation and adhesion. With the base curve and diameters of lenses being remained constant the increase in surface tension of tear film yields the increase in the adhesion between the cornea and lens while the initial rotation of lens is inversely proportional to the surface tension of the tear film.

• Korean Journal of Optics and Photonics
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• v.17 no.5
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• pp.420-429
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• 2006

In the zoom lens of digital still cameras with the variation of the image plane generated by various symmetric error factors such as curvature, thickness and refractive index error of each lens surface about the optic axis, we induce a theoretical condition to fix constantly the image plane by translating the compensator group of the zoom lens by using the Gaussian bracket. We confirm the validity of this condition by using three examples of general zoom lens types with 3, 4, and 5 groups, respectively. When these error factors are randomly changed within the range of tolerance according to the Monte Carlo method, we verify that the distributions of the degree of moving of the compensator are normal distributions at three zoom lens types. From capability analysis using these results, we theoretically propose the method estimating the standard deviation, that is, sigma-level, as a function of the maximum movement of the compensator.

• Korean Journal of Optics and Photonics
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• v.9 no.5
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• pp.282-290
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• 1998

The equivalent lens conversion technique is applied to design achromatic doublet and aplanatic doublet. A thin doublet which has zero axial thicknesses, are corrected for the third order aberrations at first, and the thin doublet is converted into thick lens system by using the equivalent lens conversion. Two types of cemented doublets, the Fraunhofer type and the Steinheil type, are designed by using a crown glass BaK-2 and a flint glass SF-2. In the thin doublet design, there are two achromatic solutions and a aplanatic solution for the both types.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.151-151
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• 2020

표면영상유속측정법은 영상을 이용한 비접촉식 유속 측정 방법으로 카메라 외에 별도로 고가의 장비를 구매할 필요가 없을 뿐 아니라 현장 상황을 영상으로 확인할 수 있기 때문에 현장조사인력이 필요 없어 경제적이고, 안전하다는 장점을 갖고 있는 하천 유속 측정 방법이다. 표면영상유속측정법은 일반적으로 상호상관법을 이용하여 수표면을 촬영한 연속된 두 영상에서 입자군의 명암값 분포를 계산하여 입자군의 변위를 계산하고 이를 두 영상 사이의 시간 간격으로 나누어 입자군의 이동 속도를 산정하는 방법이다. 따라서 표면영상유속측정법으로 산정한 유속의 정확도를 높이기 위해서는 영상 내 두 입자군의 변위를 정확하게 계산하는 것이 무엇보다 중요하다. 즉, 분석하고자 하는 영상의 물리거리를 정확하게 계산할 수 있어야 한다. 카메라를 이용하여 실제 하천 영상을 촬영한 영상은 카메라 렌즈에 의한 왜곡이 필연적으로 발생하게 되고 이는 영상 내의 변위 산정 시에도 영향을 미친다. 특히 드론을 활용하여 넓은 하천 영역을 촬영할 경우 카메라 렌즈에 의한 왜곡은 실제 물리 변위 계산 정확도에 큰 영향을 미치게 된다. 이에 본 연구에서는 카메라 왜곡이 영상 내 변위 산정 결과의 정확도에 미치는 영향을 분석하였다. 연구 결과 카메라 렌즈 왜곡은 영상 중심에서 방사방향으로 점점 크게 발생하고 왜곡 정도는 비선형적으로 나타났으며, 변위 측정 오차는 영상의 중앙부에서는 거의 차이가 없었으며, 영상 외곽부에서 최대 오차가 발생하는 것으로 나타났다. 그리고 카메라 렌즈 왜곡 보정을 실시하게 되면 영상 전체적으로 변위측정 오차는 모두 제거할 수 있는 것으로 확인하였다. 따라서 카메라 렌즈 왜곡 보정을 실시하여 표면영상유속 측정 결과의 정확도를 개선할 수 있는 것으로 나타났다. 향후 카메라 렌즈 왜곡 보정을 실시한다면 하천의 표면유속을 보다 정확하게 측정할 수 있을 것으로 기대한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.2
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• pp.177-182
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• 2015

General method for correcting the distortion caused by the characteristic of the fish-eye lens may be classified in two ways. The first method is a calibration method using a mathematical model taking into account the characteristics of the lens, the second method is a method using only the distortion correction image, regardless of the lens. When considering the characteristics of the lens, calibration equation can be calculated geometrically from the relationship between the three-dimensional real-world coordinates and two-dimensional image coordinates and the parameters of lens. However, it is not suitable for ellipsoid type lens, because of existing research papers have been corrected on the spherical-type fisheye lens. In this paper, we propose a method for correcting geometrically using fish-eye lens as an ellipsoid model. Through a calibration picture, it can be seen that the proposed method is valid.