Introduction
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There are well-established design rules for choosing a lens. There are fewer such rules for lighting, yet proper lighting is as important as using the correct lens to form useful images. For a feature to appear in an image, light must come from the illuminator, reflect off the object and be collected by the lens (figure 11). If the light to populate a given ray is not available from the illuminator, that ray will not be part of the image.
In our daily experience, we use light from the environment to see. In machine vision applications, light from the environment is a danger, because it may change when we least expect it. we need to provide controlled light in a manner that accentuates features we care about and minimizes distracting features. Vision lighting and imaging optics are best designed together as a system. The illuminator should launch all rays that can be collected by the lens as part of an image. At the same time, it should not launch rays that will never be part of an image (e.g., those rays that fall outside the field of view of the lens). These extra rays can only contribute to glare, which reduces image contrast. Unless the lighting and imaging optics are designed together, the match between them is difficult to achieve.
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Machine Vision Guide © 2003, Melles Griot. All rights reserved.
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