Optics

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SELECTION OF THE APPROPRIATE OPTICS

The selection of an appropriate lens is essential: not the test object as such is captured and processed by the software, but a video image - an image which the optics on the sensor captures and which is "interpreted" by the camera sensor. All components like lighting, the test object, a suitable filter, the camera sensor and, in particular, the optics is significantly involved in the "picture" visible and evaluable on the monitor.

In practice, each lens has varyingly strong optical faults, depending on the quality, which are adopted in the image information. Several per cent of distortion, for instance, (geometric fault as barrel or pincushion distortion) are common for standard optics. Therefore the measuring results will vary by this fault tolerance, provided that there are no subsequent calibrations on the software side.

Typical types of lenses

Entocentric standard optics (For normal use)
Telecentric measuring lenses (Fo precise measuring tasks)
colour-corrected lenses (for coloured objects and colour applications, but also for use of non-monochromatic white light) as well as IR or UV lenses
zoom lenses (mainly used in laboratories, motorised zoom lenses in machine vision applications are rarely usefully applicable)
macro lenses and microscope optics (for smallest image details)

Selection of the appropriate optics

There are a few things to consider when choosing the right lens:

Firstly, the lens must fit the existing camera. There are different types of mounts, such as C-mount, CS-mount, S-mount, F-mount, M42 to M72. With the exception of F-mount (Nikon bayonet), all lenses can generally be screwed in with a fine thread.
Put simply, all you need to do is calculate the correct focal length of the lens for a given working distance and make sure that the lens can expose the sensor to fill the format (sufficiently large image circle diameter).
However, optical details such as resolution, MTF, coatings, etc. and especially the type of optical imaging should also be taken into account in order to obtain the best possible image for evaluation.

Important lens selection criteria

Size of the test object and the object range to be detected
Sensor size (imaging size; defined by the camera)
Distance between lens and sensor (defined by the camera manufacturer, various standards with different flange back distances are common here, such as C-mount, CS-mount, F-mount).
Type of camera sensor (pixel size = required resolution of the optics, as well as sensor-specific details like micro-lenses etc.)
Required optical path (entocentric or telecentric)
Lens speed / aperture of the lens / required depth of field
Wavelength of light (monochromatic-coloured/ white mixed light, daylight/ IR/ UV)

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