China
Africa
Explore chapters and articles related to this topic
Light
Published in David M. Scott, Industrial Process Sensors, 2018
A pinhole is an aperture made from a thin metal foil with a precision hole drilled at the center; the diameter of the hole is typically in the range of 1 μm to 100 μm. An important application of pinholes is to provide spatial filtering of a laser beam. Most light sources, including lasers, do not provide a beam with a smooth intensity contour. Optical defects in the system and dust in the air create spatially dependent variations in the light intensity, and these imperfections degrade the quality of the image or measurement. This spatial noise can be filtered out by passing the light through a lens and placing a pinhole at its focus. Since the lens creates a two-dimensional Fourier transformation of the incident light beam, all of the low spatial frequencies are concentrated at the center of the focus. The pinhole removes the higher spatial frequencies, which contain all of the noise components. The resulting light, which can be recollimated with another lens, is more uniform in intensity than the original beam.
2+ Imaging
Published in Francesco S. Pavone, Shy Shoham, Handbook of Neurophotonics, 2020
Tobias Nöbauer, Alipasha Vaziri
In contrast to a pinhole camera, a photographic camera with a focusing lens collects rays from a range of angles for each source point and thus is capable of capturing more light than a pinhole camera. The angular directions of the rays, however, do not get recorded, but rather averaged over, which is just what leads to blur outside of the focal plane. In a typical photographic camera, an adjustable iris diaphragm is placed in the optical path such that it allows adjustment of the range of incident ray angles being captured. Such an element, known as the aperture stop, allows a choice between a quasi-pinhole mode (aperture stop closed, small range of ray angles captured, deep DOF), and a wide-open mode (iris opened, large range of ray angles captured, shallow DOF).
Wavenumber Transforms
Published in David C. Swanson, ®, 2011
Consider the pinhole camera in Figure 8.1. On any given spot on the outside of the camera box, the light scattered from the field produces a “brightness” wavenumber spectrum. Another way to look at the physics is that light rays from every object in the field can be found on any given spot on the outside of the camera box. By making a pinhole, the camera box allows reconstruction of the object field as an upside-down and left–right reversed image on the opposite side of the pinhole on what we call the focal plane.
An automatic calibration algorithm for endoscopic structured light sensors in cylindrical environment
Published in Nondestructive Testing and Evaluation, 2023
Mohand Alzuhiri, Zi Li, Jiaoyang Li, Adithya Rao, Yiming Deng
The magnitude of is set to have a large positive value that ensures the intersection of the with the cylinder (Empirically, was always set to be larger than 10). To calculate (), the ray-cone intersection () algorithm is used. finds the intersection points between the input rays () and the estimated cone model. A detailed description of the ray-cone intersection () process is described in Section 6.1. The estimated camera points () are then created by projecting from the 3D space to image coordinates with a pinhole camera model (PHM). The pinhole camera is a projection camera model that describes the projection of the points from the 3D world to the 2D coordinates of the camera sensor (assuming a distortion-free imaging lens). The pinhole camera model concept is explained later in the paper and is mathematically described in Eq. 10. With both the input data and estimated data in the camera image domain, the minimisation problem can be described by
Minimal Detection Time for Localization of Radioactive Hot Spots in Low and Elevated Background Environments Using a CZT Gamma-Ray Spectrometer
Published in Nuclear Technology, 2022
Lowie Brabants, Mattias Simons, David de Schepper, Eric Demeester, Wouter Schroeyers
Typically, pinhole cameras offer a wide energy range and good angular resolution but are heavy, have a small field of view, and have extremely low sensitivity. On the other hand, coded-aperture cameras have a higher sensitivity as they use a coded mask with multiple holes arranged in a particular order, but they require an additional decoding step. They achieve similar characteristics to a pinhole camera in angular resolution and field of view. The third category, Compton cameras, makes use of the kinematics of Compton scattering to localize radiation sources without using collimators. As a result, Compton cameras have an optimal field of view (up to 360 deg) and high-energy resolution. A downside to the Compton cameras is that they have a limited angular resolution and are not able to localize gamma rays with energies below 250 keV (Ref. 9).