Telecentric entrance pupil - Optics

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Discussion Overview

The discussion centers on the concept of telecentric systems in optics, specifically focusing on the characteristics of the entrance pupil and the challenges associated with ray-tracing through such systems. Participants explore the implications of the paraxial approximation and geometrical optics in relation to the behavior of aperture stops within these systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant notes that an object-telecentric system has an entrance pupil that is infinitely far away, which is achieved by placing an aperture stop at the focal point of a lens.
  • The same participant expresses difficulty in ray-tracing the aperture stop through the telecentric system without assuming the aperture stop has a diameter approaching zero.
  • Another participant suggests that the paraxial approximation might be a reason for the difficulties encountered in understanding the entrance pupil condition.
  • Some participants reference external resources for additional information on telecentric lenses, indicating that they do not find the concept particularly bizarre.
  • There is a reiteration of the idea that, under the paraxial approximation, any object at a focal point will produce an image infinitely far away, with the aperture acting as the object in this scenario.
  • A participant requests assistance with another optics-related thread, indicating a broader context of inquiry regarding entrance and exit pupils.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the challenges of ray-tracing in telecentric systems, as some express uncertainty about the implications of the paraxial approximation while others provide additional resources without resolving the initial query.

Contextual Notes

The discussion involves assumptions related to the paraxial approximation and geometrical optics, which may not be fully articulated or universally accepted among participants. The dependence on the diameter of the aperture stop is also a point of contention.

Wminus
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Hi. As you guys know, an object-telecentric system (a system with constant magnification) has per definition an entrance pupil that is infinitely far away. One can construct such a system by taking a lens and placing an aperture stop (AS) at its focal point.

My issue is that I am struggling to ray-trace the aperture stop (AS) through the telecentric system. I just can't get the "infinitely far away entrance pupil" condition without also assuming that the aperture stop has a diameter approaching zero.

I am assuming paraxial approximation and geometrical optics. Is perhaps this the reason behind my difficulties?
 
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Andy Resnick said:
Not sure- there's nothing particularly bizarre about telecentric lenses. Here's some additional info that may help you:

http://www.lhup.edu/~dsimanek/3d/telecent.htm

https://www.schneideroptics.com/ecommerce/CatalogSubCategoryDisplay.aspx?CID=1439
I think I forgot about the paraxial approximation. With thin lenses and paraxial approximation, any object at a focal point will produce an image infinitely far away from the lens. In this case the object is the aperture, and hence its image will be infinitely far away.

Anyway, if you are skilled with optics, could you please help me here? https://www.physicsforums.com/threads/optics-Newtonian-telescope.804709/ I simply can't seem to find the entrance and exit pupils!
 
Wminus said:
I think I forgot about the paraxial approximation. With thin lenses and paraxial approximation, any object at a focal point will produce an image infinitely far away from the lens. In this case the object is the aperture, and hence its image will be infinitely far away.

Anyway, if you are skilled with optics, could you please help me here? https://www.physicsforums.com/threads/optics-Newtonian-telescope.804709/ I simply can't seem to find the entrance and exit pupils!

I don't know about 'skilled', but I responded to the above thread...
 
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