In machine vision systems, a good lens is like a good eye for a person. A good lens performs well in terms of resolution, sharpness, and depth of field, and corrects various aberrations effectively, but its price will also increase several times or even hundreds of times.
By understanding certain patterns and gaining experience, one can avoid some losses when selecting lenses for system setup, leading to better system performance. Below is a brief introduction to the interrelationships between various parameters of machine vision lenses:
1. The influence of focal length:
• The smaller the focal length, the greater the depth of field;
• The smaller the focal length, the greater the distortion;
• The smaller the focal length, the more severe the vignetting phenomenon, which reduces the illumination at the edges of aberrations;
2. The impact of aperture size:
• The larger the aperture, the brighter the image;
• The larger the aperture, the shallower the depth of field;
• The larger the aperture, the higher the resolution;
3. Image field center and edge:
• Generally, the center of the image field has higher resolution than the edges;
• Generally, the light field illuminance is higher at the center of the image field than at the edge;
4. The effect of light wavelength:
Under the same camera and lens parameters, the shorter the wavelength of the light source, the higher the resolution of the resulting image. Therefore, in vision systems requiring precise dimensional and position measurements, using short-wavelength monochromatic light as the illumination source can significantly improve system accuracy.
