Frequently Asked Questions about Telecentric Lenses




Telecentric lenses are industrial lenses with high definition and low distortion, often used for precision parts measurement.This article summarizes some of the questions that will be involved in the use of telecentric lenses and answers them.Hope this gives you a better understanding of telecentric lenses.




No distortion in telecentric lenses?

When many people mention telecentric lenses, their first reaction is that telecentric lenses have no distortion.The correct statement would be that telecentric lenses have no parallax,telecentric lenses have the main ray of light incident on each field of view parallel to the optical axis, thus eliminating parallax.That is, the size of the object when observing within the depth of field does not vary with the working distance (strictly speaking, the amount of variation is very small).Telecentric lenses are therefore ideally suited for high-precision measurements.




Can the depth of field of a telecentric lens be adjusted at will?


Based on the depth-of-field formula:


Depth of field = 2*(permissible circle of confusion * effective^2) = permissible circle of confusion/(NA*magnification)


For fixed-magnification telecentric lenses, the magnification is a fixed value. If you want to increase the depth of field, you can increase the effective or decrease the N.A. This is easier to achieve for the lens, although the resolution will be reduced accordingly.




How to select a telecentric lens?


The working distance and external dimensions can be determined according to the actual use requirements.If the camera selection has been completed, you can first select a lens series that supports this camera target surface, and then determine the magnification of the lens by the ratio of the camera target surface 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 to the pixel size through the magnification to determine whether it matches the camera.If you want the best resolution to match your camera, you can get it directly by converting pixel size to magnification.The lens specification table generally gives the minimum depth of field, if the depth of field is not enough, you can lose resolution to change the appropriate size.If you want a smaller depth of field, you need to re-select a lens with a larger NA.



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