A part from lighting considerations, correct optics contribute greatly to the proper performance of a machine-vision system. Moreover, with an increasing number of solid-state cameras becoming available, choosing the optics for a particular imaging application has become a challenging task. Fortunately, various types of lenses are currendy offered for systems developers, including micro, standard, zoom, and telecentric lenses, that can be implemented for specific applications. In choosing optics for an imaging system, several key parameters must be addressed. They include the minimum feature size to be detected, the field of view (FOV) or the area to be imaged, the distance from the camera sensor to the object, the type of image sensor used, and the required depth of field. Proven optics and lens formulas can be used to determine the needed parameters of the lens. In C-mount lens designs, for example, the detector is placed 0.690-in. behind the cameras front flange. Accordingly, when the focus ring is set to infinity, the detector is at the back focus of the lens. This approach simplifies the process of distance calculations, especially when determining the length of an extension or spacer between the camera and lens.
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