Aperture Stops, Entrance Pupils & Exit Pupils

[toam]

I'm doing an assignment involving an optics question.

There is a lens (diameter 4cm, focal length 5cm) an apeture (diameter 5cm, position 2cm in front of lens) and an object (1.5cm high, 8cm in front of lens).

Now I have determined that the lens is the aperture stop. Now, because the lens is the aperture stop the aperture does not limit the incoming light at all and this leads me to believe that the lens is the entrance pupil. Since the lens is the entrance pupil the lens must also be the exit pupil since it can't make an image of itself.

Is this an acceptable situation to have? I assume it is because it makes the aperture completely redundant and unnecessary and therefore is equivilent to the same system without an aperture, but I can't find any examples in books or lecture notes where this occurs...

 

[andrevdh]

You are correct in your reasoning. See the section on Front Stops in "Fundamentals of Optics" by Jenkins and White.

 

[ogb p]

I can confirm that this is indeed an acceptable situation to have. The lens being the aperture stop means that it controls the amount of light entering the system, and since it is the only element in the system, it also acts as both the entrance and exit pupil. This is a common occurrence in optical systems, especially in simple ones like the one described in your assignment.

Having the lens act as both the entrance and exit pupil does make the aperture redundant, but it does not make it unnecessary. The aperture still plays a role in controlling the depth of field and the amount of aberrations in the image. Additionally, having a larger aperture can also improve the overall image quality by allowing more light to enter the system.

While it may be difficult to find specific examples of this exact situation in books or lecture notes, it is a common concept in optics and is often used in basic optical systems. It is important to understand the role of the aperture stop, entrance pupil, and exit pupil in order to properly design and analyze optical systems. I hope this helps with your assignment.