Telecentric entrance pupil - Optics

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In summary, an object-telecentric system has an entrance pupil that is infinitely far away. One can construct such a system by taking a lens and placing an aperture stop at its focal point. However, when using thin lenses and paraxial approximation, any object at a focal point will produce an image infinitely far away from the lens. If you are skilled with optics, you can help find the entrance and exit pupils of the system.
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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!
 
  • #4
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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What is a telecentric entrance pupil?

A telecentric entrance pupil is a type of optical system that has a pupil (the aperture through which light enters) located at or near the front of the system and is perpendicular to the optical axis. This means that all rays of light passing through the entrance pupil are parallel to each other, resulting in a distortion-free image.

How does a telecentric entrance pupil work?

In a telecentric entrance pupil system, the entrance pupil is placed at or near the front of the system and is perpendicular to the optical axis. This allows all rays of light entering the system to be parallel to each other. This results in a distortion-free image, as any deviation from parallel rays would result in distortion.

What are the advantages of using a telecentric entrance pupil?

One of the main advantages of using a telecentric entrance pupil is that it produces distortion-free images. This is especially useful in applications where high precision is required, such as in metrology or medical imaging. Additionally, telecentric entrance pupils can reduce the effects of depth of field, making them ideal for measuring or imaging objects with varying heights.

What are some common applications of telecentric entrance pupils?

Telecentric entrance pupils are commonly used in metrology, medical imaging, and machine vision applications. They are also used in microscopy, where distortion-free images are crucial for accurate measurements. Additionally, telecentric entrance pupils are used in high-precision measurement devices such as coordinate measuring machines (CMMs) and laser scanners.

How do I choose the right telecentric entrance pupil for my application?

Choosing the right telecentric entrance pupil for your application depends on various factors such as the object size, working distance, and required accuracy. It is important to consult with an expert in optics to determine the best telecentric entrance pupil for your specific needs.

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