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)

Tip:
Online wizards for optical calculations can be found in the "Service" area.

Selection of the appropriate optics

Several things must be observed in order to select the appropriate optics:

First of all, it must be possible to mount the optics to the existing camera. There are different connection types like C-mount, CS-mount, S-mount, F-mount, M42 to M72. Except for the F-mount (Nikon bayonet), all optics can usually be screwed in by means of a fine thread.

In simple terms, only the appropriate focal length of the lens must be calculated for a certain working distance and the lens must be capable to expose the full size of the sensor (sufficient image circle diameter).

However, also the optic details like resolution, MTF, coatings, etc. and in particular the type of the optic imaging should be considered in order to achieve an image as perfect as possible for the 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)
• Working distance between test object and optics (attention - normally the distance to the optic centre of the system is counted, not the front edge of the lens)
• Working distance between test object and optics (attention - normally the distance to the optic centre of the system is counted, not the front edge of the lens)
• 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)
• Luminous intensity / aperture of the lens / required depth of field
• Wavelength of the light (monochromatic coloured / white blended light, daylight / IR / UV)

Conclusion:
The image produced is the basis for all further software evaluations. Therefore it is worthwhile to optimise the image as much as possible by using reasonable hardware! Please do not forget the lens!