How does a telecentric lens achieve no parallax?




Many people mention telecentric lenses, the first reaction is that telecentric lenses do not have aberrations, the correct statement should be that telecentric lenses do not have parallax, that is, when observing within the depth of field, the size of the object will not change with the change in the working distance (technically speaking, the amount of change is very small), so telecentric lenses are very suitable for high-precision measurement field.



How does a telecentric lens achieve no parallax?



This is mainly ensured by the optical design architecture of the lens, common lenses, such as FA lenses, the main light ray of the off-axis incident light line is with a divergence angle, and the smaller the focal length, the greater the divergence angle, the greater the parallax, but telecentric lenses for each field of view of the main light ray of the incident light line is parallel to the optical axis, thus eliminating parallax. (It is worth stating that it is not parallel light incidence, if it is parallel light incidence, it means that the object is at infinity).



When selecting telecentric lenses, the working distance and external dimensions can be determined according to the actual use requirements. If the camera has been selected, you can first select the telecentric lens series that supports the target surface of this camera, and then determine the magnification of the lens by the ratio of the target surface of the camera to the size of the field of view to be observed.



The resolution can be selected according to the actual need, but it is necessary to convert the magnification to the pixel size to determine whether it matches the camera. If you want to match the camera with the best resolution, you can directly through the pixel size and magnification conversion to get. Lens specification table generally gives the minimum depth of field, if the depth of field is not enough, you can lose the resolution of the appropriate change to a larger, if you want a smaller depth of field, you need to re-select the NA larger lens.

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