Suitable lenses for high precision machine vision High-precision machine vision applications depend on the production of high-quality, reproducible images, whether for inspection or measurement purposes. This means that images must have sufficient resolution and correct definition of the areas of interest for inspection or measurement to occur. Each element of a machine vision system has an important role to play in the overall result, but the optical device is the heart of it since it is responsible for forming the image on the camera sensor.

The construction characteristics of the optical system within the lens (such as the size of the lens radius, the distance between the lenses, or the type of glass used) as well as the distance between the lens and the sensor have a direct impact on the image quality.

Factors affecting lens performance Once the field of view of the application is determined, resolution and image quality are the most important selection criteria. Most machine vision lenses are endocentric, fixed-focus lenses that provide the same perspective as the human eye. With perfect optics, all light rays incident on the sensor are focused from a single point at the object to a single point at the image. However, all lenses suffer from imperfections that influence the resolution and quality of the image produced by the lens. We find for example:

Physical defects. Surface defects will cause light rays to focus at a different point, resulting in blurring.

Chromatic aberrations. The angle of refraction of light through a lens depends on the wavelength, resulting in colored bangs on all images produced with white light with blurring at the edges of the image.

Spherical aberrations. Most lenses are spherical. Thus, the focal point of each ray passing through the lens depends on the distance from the center of the lens. The resulting images will become increasingly blurred as they approach the edges.

Spatial distortion. All lenses suffer from some distortion in which the image is stretched or compressed in a non-linear fashion, making accurate measurements difficult. In general, shorter focal length lenses suffer more distortion than longer focal length lenses, because the light strikes the sensor from a wider angle.

Non-uniform illumination and shading across the image. With any lens, the brightness of the image is reduced toward the edges and this is called vignetting. Cos4 vignetting occurs because the light has to travel further to the edge of the image and reach the sensor at a lower angle. Mechanical vignetting occurs when the light beam is blocked mechanically, usually by the lens mount.

For more information:

トップ   編集 凍結 差分 バックアップ 添付 複製 名前変更 リロード   新規 一覧 単語検索 最終更新   ヘルプ   最終更新のRSS
Last-modified: 2021-10-09 (土) 11:36:54 (14d)