Aperture stop for an optical system

In summary, the aperture stop (AS) of an optical system limits the amount of light from the object and is determined by the on-axis object point. The AS may change if the object moves along the optical axis, indicating that it is not a fixed aperture but rather depends on the position of the 3D object being imaged. However, in some cases, such as setting a specific aperture on a camera lens, the AS remains fixed regardless of the object's position.
  • #1
fog37
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Hello Forum,

The aperture stop (AS) of an optical system is that physical aperture in the system that limits the amount of light from the object.
Consider a 2D object formed by point objects. The AS is determined by considering the object point that is located on the optical axis. Will the AS for that on-axis point also represent the AS for all the other off-axis objet points forming the object?

If the same 2D object moves to a different position along the optical axis, the AS will change since it is determined by the on-axis object point and its location, correct?

If that is correct, it seems that the AS is not fixed aperture for the optical system but strongly depends on the position of the 3D object being imaged...

Thanks,
fog37
 
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  • #2
fog37 said:
If the same 2D object moves to a different position along the optical axis, the AS will change since it is determined by the on-axis object point and its location, correct?

not sure how you come to that conclusion. If I set a f2.8 aperture on my camera lens. it stays at f2.8 regardless of how far or close an object is to the lens or whether it in the axis line of the lens or off to one side of that axis

fog37 said:
If that is correct, it seems that the AS is not fixed aperture for the optical system but strongly depends on the position of the 3D object being imaged...

refer to my previous comment

cheers
Dave
 

1. What is an aperture stop for an optical system?

The aperture stop for an optical system is a physical opening that controls the amount of light that enters the system. It is typically located in the lens of a camera or telescope and determines the size of the light beam that reaches the image plane.

2. What is the purpose of an aperture stop?

The aperture stop serves two main purposes in an optical system. Firstly, it controls the amount of light that enters the system, allowing for proper exposure and image quality. Secondly, it also determines the depth of field or the range of distances that appear in focus in the final image.

3. How is the size of an aperture stop determined?

The size of an aperture stop is determined by the diameter of the opening, measured in units of length such as millimeters or inches. This size can be manually adjusted on some systems, while others have a fixed size determined by the design of the lens.

4. What happens if the aperture stop is too large or too small?

If the aperture stop is too large, it will allow too much light to enter the system, resulting in overexposure and potentially washed out images. If the aperture stop is too small, it will limit the amount of light entering the system, resulting in underexposed images. Additionally, the size of the aperture stop also affects the depth of field, with a larger stop resulting in a shallower depth of field and vice versa.

5. Can the aperture stop be changed in an optical system?

In most cases, yes, the aperture stop can be changed in an optical system. This can be done manually on some systems by adjusting the size of the opening, while others may have a fixed stop but offer interchangeable lenses with different sized stops. In some advanced systems, the aperture stop can also be electronically controlled through the camera or telescope's software.

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