Korean Journal of Optics and Photonics (한국광학회지)

Optical Society of Korea (한국광학회)
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Catadioptric Omnidirectional Optical System Using a Spherical Mirror with a Central Hole and a Plane Mirror for Visible Light

중심 구멍이 있는 구면거울과 평면거울을 이용한 가시광용 반사굴절식 전방위 광학계

  • Seo, Hyeon Jin (Department of Photonics and Sensors, Hannam University) ;
  • Jo, Jae Heung (Department of Photonics and Sensors, Hannam University)
  • 서현진 (한남대학교 공과대학 광.센서공학과) ;
  • 조재흥 (한남대학교 공과대학 광.센서공학과)
  • Received : 2015.03.12
  • Accepted : 2015.04.01
  • Published : 2015.04.25
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Abstract

An omnidirectional optical system can be described as a special optical system that images in real time a panoramic image with an azimuthal angle of $360^{\circ}$ and the altitude angle corresponding to the upper and lower fields of view from the horizon line. In this paper, for easy fabrication and compact size, we designed and fabricated a catadioptric omnidirectional optical system consisting of the mirror part of a spherical mirror with a central hole (that is, obscuration), a plane mirror, the imaging lens part of 3 single spherical lenses, and a spherical doublet in the visible light spectrum. We evaluated its image performance by measuring the cut-off spatial frequency using automobile license plates, and the vertical field of view using an ISO 12233 chart. We achieved a catadioptric omnidirectional optical system with vertical field of view from $+53^{\circ}$ to $-17^{\circ}$ and an azimuthal angle of $360^{\circ}$. This optical system cleaniy imaged letters on a car's front license plate at the object distance of 3 meters, which corresponds to a cut-off spatial frequency of 135 lp/mm.

전방위 광학계는 360도의 방위각과 지평선 위와 아래의 수직화각에 대한 상을 동시에 결상이 가능한 광학계이다. 본 논문에서는 제작을 쉽게 하면서 크기가 작아지도록 하기 위해서 가운데에 구멍이 뚫려있는 옵스큐레이션(obscuration)을 갖는 구면거울 1장과 평면거울 1장으로 이루어진 거울계 및 이 거울계에서 반사하여 구면거울의 옵스큐레이션을 통과한 시야각 범위 안의 광을 결상하는 구면렌즈 3개와 하나의 구면 이중렌즈로 구성된 결상렌즈계를 사용하는 가시광용 반사굴절식 전방위 광학계를 설계하고 제작하여 전방위 영상을 실제로 결상하였다. 그리고 자동차 앞, 뒷번호판의 영상을 보고 이 전방위 광학계의 통과 공간주파수를 측정하고, ISO 12233 차트의 영상으로부터 전방위 광학계의 수직화각을 측정하여 광학계의 성능을 평가하였다. 이 결과 전방위 광학계의 수직화각은 $+53^{\circ}{\sim}-17^{\circ}$이며, 방위각은 $360^{\circ}$이고, 3 m 거리에서 자동차 앞번호판의 숫자를 구별할 수 있었는데, 이는 135 lp/mm의 통과 공간주파수에 해당한다.

Keywords

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