• Proceedings of the Optical Society of Korea Conference
• /
• 1990.02a
• /
• pp.82-86
• /
• 1990

A camera type optical bench system equipped with a lens collimator and an image analyzer is fabricated to measure the equivalent focal length and distortion of lenses. This system is automatized by the computer which controls stepping motors. A nodal slide optical bench system equipped with an off axis reflective collimator is fabricated and improved by using rotating arms and air bearing system. distortion measurement on a wide angle lens using the camera method and the nodal slide method is reported. Defocusing error in the distortion measurement with the nodal slide optical bench is analyzed and improved by iteration method to search the correct image point.

• Journal of the Korean Solar Energy Society
• /
• v.22 no.3
• /
• pp.31-37
• /
• 2002

This experimental study represents the results of an analysis on the characteristics of flux density distributions in the focal region of solar concentrator. The characteristics of flux density distributions are investigated to optimally design and position a cavity receiver. This deemed very useful to find and correct various errors associated with a dish concentrator. We estimated the flux density distribution on the target placed along with focal lengths from the dish vertex to experimentally determine the focal length. It is observed that the actual focal point exists when the focal length is 2.17 m. We also evaluated the position of flux centroid, and it was found that there were errors within 2 cm from the target center. The total integrated power of 2467 W was measured under focal flux distributions, which corresponds to the intercept rate of 85.8%. As a result of the percent power within radius, approximately 90% of the incident radiation is intercepted by about 0.06 m radius.

• 한국전산유체공학회:학술대회논문집
• /
• 2009.04a
• /
• pp.170-175
• /
• 2009

Shock focusing is related with explosive release of shock wave energy on a narrow spot in a short duration of time triggering a spontaneous high pressure near the focal point. It is well known that reflection of planar incident shock wave from the metallic concave mirror such as ellipsoidal, paraboloidal or hemispherical cavities will focus on a focal point. We intend to improve the computational results using a wave propagation algorithm and to resolve the mushroom-like structure. For computation of the concave cavity flow, it is not easy to use a single-block mesh because of the many singular points in geometry and coordinates. We have employed a uniform Cartesian-grid method for the wave propagation algorithm.

• Laser Solutions
• /
• v.14 no.2
• /
• pp.13-16
• /
• 2011

We fabricated the Fresnel zone plate using femtosecond laser lithography-assisted micro-machining, which is a combined process of nonlinear lithography and wet etching. We investigated the focusing properties by launching a 632.8nm wavelength He-Ne laser beam into the zone plate. The spot size of the primary focal point was $27{\mu}m$ and the intensity of focal point was 0.565W/$cm^2$.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2000.04a
• /
• pp.127-132
• /
• 2000

Though the increment of using computer vision system, there are lots of difficulties to measure precisely because of measurement error or distortion phenomenon. Among these reasons, the distortion of edge is dominant reason which is occurred by the blurred image. So, the problem of clear judgment about image focal point is very important. We must fix the discrimination criteria which is collected by image recognition of precise focus. To solve these problems, we compare with make processing methods using image intensity gradient, laplacian, and sum -modified laplacian operator. These experimental results showed modified mask processing method is effective.

• Korean Journal of Optics and Photonics
• /
• v.8 no.1
• /
• pp.19-25
• /
• 1997

Holographic zone plate (HZP) is fabricated by interfering a plane wave and a spherical wave in a dichromated gelatin (DCG) film obtained from Agfa 8E75HD plates. We have developed a simple theory for HZP considering optical nonlinearity of DCG material. Analysis of our theory for HZP shows that it has infinite focal points at distances f,f/2, f/3,,…. In experiment, we observed the corresponding focal points of up to f/6 when illuminating HZP by a plane wave. It is also shown that the beam profile around the first focal point measured by using a knife-edge scanning method has a Gaussian shape.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2005.05a
• /
• pp.3-7
• /
• 2005

Focal mechanism of the real and imaginary faults in the western coast of Japan has been assumed by examining the previous studies on the seismicity, seismic gap, fault behaviors, seismic zoning, and faults. In the area of no seismic information, the focal mechanism has been assumed to have the maximum influence on the tsunami height in the eastern coast of Korea. The tsunami height in a particular point of the eastern coast of Korea can vary up to 7 orders with the variation of the strike of the fault in a particular source point of the western coast of Japan with constant magnitude. Tsunami scenario DB including tile arrival times and tsunami heights has been constructing by using the assumed focal mechanism of the western coast of Japan. Tsunami warning system will be reinforced by using this tsunami scenario DB near future.

• Journal of the Korean Geophysical Society
• /
• v.8 no.2
• /
• pp.93-96
• /
• 2005

Focal mechanism of the real and imaginary faults in the western coast of Japan has been assumed by examining the previous studies on the seismicity, seismic gap, fault behaviors, seismic zoning, and faults. In the area of no seismic information, the focal mechanism has been assumed to have the maximum influence on the tsunami height in the eastern coast of Korea. The tsunami height in a particular point of the eastern coast of Korea can vary up to 7 orders with the variation of the strike of the fault in a particular source point of the western coast of Japan with constant magnitude. Tsunami scenario DB including the arrival times and tsunami heights has been constructing by using the assumed focal mechanism of the western coast of Japan. Tsunami warning system will be reinforced by using this tsunami scenario DB near future.

• Physical Therapy Korea
• /
• v.13 no.4
• /
• pp.23-29
• /
• 2006

The purpose of the present study was to examine gaze effects on spatial and kinematic characteristics during a pointing task. Subjects were asked to watch and point to an aimed target (2 mm in diameter) displayed on a vertically mounted board. Four gaze conditions were developed as combinations of "seeing-aiming" in terms of the eye movements: Focal-Focal (F-F), Focal-Fixing (F-X), Fixing-Focal (X-F), and Fixing-Fixing (X-X). Both the home target and an aimed target were presented for 1 second and then were disappeared in F-F and X-F. In X-F and X-X, only an aimed target disappeared after 1 second. Subjects were asked to point (with index finger tip) to an aimed target accurately as soon as the aimed target was removed. A significant main effect of gaze was found (p<.01) for normalized movement time. Peripheral retina targets had significantly larger absolute error compared to central retina targets on the x (medio-lateral) and z (superior-inferior) axes (p<.01). A significant undershooting to peripheral retina targets on the x axis was found (p<.01). F-F and X-F had larger peak velocities compared to F-X and X-X (p<.01). F-F and X-F were characterized by more time spent in the deceleration phase compared to F-X and X-X (p<.01). The present study demonstrates that central vision utilizes a form of on-line visual processing to reach to an object, and thus increases spatial accuracy. However, peripheral vision utilizes a relatively off-line visual processing with a dependency on proprioceptive information.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.42 no.4 s.304
• /
• pp.87-94
• /
• 2005

3D image mosaicking is useful for 3D visualization of the roadside scene of urban area by projecting 2D images to the 3D planes. When a sequence of images are filmed from a side-looking video camera passing long distance areas, the ghost effect in which same objects appear repeatively occurs. To suppress such ghost effect, the long distance range areas are detected by using the distance between the image frame and the 3D coordinate of tracked optical flows. The ghost effects are suppressed by projecting the part of image frames onto 3D multiple planes utilizing vectors passing the focal point of frames and a virtual focal point. The virtual focal point is calculated by utilizing the first and last frames of the long distance range areas. We demonstrate algorithm that creates efficient 3D Panoramic mosaics without the ghost effect at the long distance area.