Lens as aperture stop, entrance pupil, and exit pupil simultaneously

[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.