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Multiple Image Techniques
Published in Brian E. Dalrymple, E. Jill Smith, Forensic Digital Image Processing, 2018
Brian E. Dalrymple, E. Jill Smith
Light rays come to a point of focus on only one plane, the only one in sharp focus. Objects slightly in front of and behind the plane of focus appear to the human eye as sharp because it cannot discern small differences in precise focus. This range is referred to as depth of field, and it is affected by the following factors: The smaller the aperture, the greater the depth of field.The shorter the focal length of the lens, the greater the depth of field.The greater the camera-to-subject distance, the greater the depth of field.
Techniques
Published in Rajpal S. Sirohi, Introduction to OPTICAL METROLOGY, 2017
Depth of field is the distance along the optical axis over which image details are observed with acceptable clarity. Those factors that influence resolution also affect depth of field, but in the opposite direction. Therefore, a compromise must be reached between these two parameters, which is more difficult as magnification increases. The depth of field, daxial, can be estimated from daxial=λμ2−NA2NA2=λμsinθcotθ=λNAcotθ
Lenses
Published in Roshan L. Aggarwal, Kambiz Alavi, Introduction to Optical Components, 2018
Roshan L. Aggarwal, Kambiz Alavi
Typical fixed focal lengths of the camera lenses are 35, 50, and 85 mm. Typical f-numbers are 2.8, 1.8, 1.4, and 1.2. In photography, 50 mm is considered to be the normal focal length. Whenever you look through a 50-mm lens, the scene appears to be the same as seen with your own eye. A longer focal length lens magnifies the image by a factor, which is equal to the focal length divided by 50. For example, a 200-mm lens magnifies everything in the scene by a factor of 4. An 85-mm lens is referred to as the portrait lens. A 35-mm lens is referred to as the street lens. The longer the focal length, the shallower is the depth of field. A 100-mm lens at f/2.8 will have a much shallower depth of field than a 35-mm lens at f/2.8.
On the behavior of inhaled fibers in a replica of the first airway bifurcation under steady flow conditions
Published in Aerosol Science and Technology, 2022
Frantisek Lizal, Matous Cabalka, Milan Maly, Jakub Elcner, Miloslav Belka, Elena Lizalova Sujanska, Arpad Farkas, Pavel Starha, Ondrej Pech, Ondrej Misik, Jan Jedelsky, Miroslav Jicha
The precise evaluation of length of fibers is limited by the depth of field. Fibers out of the optimal focus appear shorter. The depth of field is determined by the subject distance, the lens focal length, and the lens relative aperture. For the given camera sensor size (20,48 × 20,48 mm) and the required image spatial resolution (1,3 µm/pix), the depth of field can be controlled only by changing the lens aperture. However, reducing the lens aperture (increasing f-number) reduces the amount of collected light, which severely reduces the contrast of fibers in the image. Moreover, very small apertures are likely to produce diffraction and reduce image overall sharpness. The optical setup used here was a carefully chosen compromise between depth of field, image brightness and sharpness