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Light
Published in David M. Scott, Industrial Process Sensors, 2018
A neutral density filter is one that reduces the intensity of light equally at all wavelengths over a large portion of the spectrum. The filters are specified in terms of their optical density, which is the negative common logarithm of the transmission coefficient. Therefore, the intensity If of the transmitted light as a fraction of the incident light I0 is given by () If=I010−(OD)
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Published in Bethe A. Scalettar, James R. Abney, Cyan Cowap, Introductory Biomedical Imaging, 2022
Bethe A. Scalettar, James R. Abney, Cyan Cowap
[Neutral Density Filters] Microscopes use a variety of filters to control the quantity and nature of light. Neutral density (ND) filters are used to reduce the amount of light incident on the sample and/or detector. They are called ND filters because they are spectrally neutral: they reduce light equally across all visible wavelengths. ND filters are typically characterized by a single number called “optical density” (OD) that describes the amount of light that the filter transmits (the transmittance, T): T=10-ODOD=-logTCalculate the amount of light transmitted through ND filters having the following common ODs: 0.1, 0.2, 0.3, 0.5, 1.0, 1.5, and 2.0.Most ND filters are absorptive: they block light by absorbing it. What happens to the energy from the absorbed light?Optical densities, unlike transmittance, are additive. Thus, when multiple filters are used, the total OD is simply the sum of the individual ODs. Calculate the OD necessary to block 75% of the incident light. Which combination(s) of filters from part (a) can be used?
Filters
Published in Solomon Musikant, Optical Materials, 2020
The neutral density filter attenuates light without changing its spectral quality. One way of specifying a neutral filter is by optical density (OD), where OD is defined by the following relation: OD=log101/T
The Nyquist criterion and its relevance in phase-stepping digital shearography: a quantitative study
Published in Journal of Modern Optics, 2022
Awatef Rashid Al Jabri, Kazi Monowar Abedin, S. M. Mujibur Rahman
The schematic diagram of the phase-stepping shearography experiments is shown in Figure 1. Coherent light from a 20 mW, polarized, helium–neon laser was expanded by a 40× beam expander (microscope objective), and the light illuminates the test object, which has an optically rough surface. The light scattered by the test object is incident on a modified Michelson interferometer, located about 40 cm away. The optical path lengths of the two arms of the Michelson interferometer were balanced to approximately 2 mm. A 50 mm non-polarizing cubic beamsplitter was used in the interferometer. One mirror of the Michelson interferometer was tilted by a given amount to produce a known amount of image shear in the horizontal direction. A high-resolution digital camera (Nikon D5300) was used do capture the sheared images. The camera has a 24 Megapixel CMOS image sensor with physical dimensions of 23.5 mm × 15.6 mm, and a native pixel resolution of 6000 × 4000 pixels. The pixel size on the camera sensor is 3.9 µm × 3.9 µm. An AF-P DX Nikkor zoom lens of 18–55 mm focal length was attached to the camera. A neutral-density (ND) filter was used to control the amount of light entering the camera and to prevent any possible saturation of the image sensor. An USB cable directly connected the camera to a desktop PC. All the camera functions such as shutter operation, exposure setting, aperture setting, etc. could be controlled from the PC using the appropriate software. In the present experiments, the camera was operated in the aperture priority mode selected by the mode dial of the camera, which enabled us to control the speckle size on the camera sensor by the software. The camera then selects the shutter speed automatically to generate the best possible image. The autofocus function was disabled, and manual focus mode was chosen for the present experiments. In order to change the speckle size on the image sensor, we selected different F numbers discretely from the camera control software on the PC.