Numerical Aperture and Acceptance Angle The numerical aperture (NA) of a lens or optical fiber is a measure of its ability to collect and focus light ont...
The numerical aperture (NA) of a lens or optical fiber is a measure of its ability to collect and focus light onto a small spot. It is a dimensionless quantity that ranges from 0 to 1, with 1 representing a perfect, circular aperture.
The acceptance angle is the half-angle subtended by the aperture. It is equal to the angle between the center of the aperture and the point on the object's focal plane that is closest to the lens.
Numerical aperture and acceptance angle are related by the following equation:
where:
a is the radius of the aperture
d is the distance from the center of the aperture to the focal point
In simpler terms:
A lens with a higher NA collects more light and focuses it more accurately.
A lens with a smaller acceptance angle has a narrower view angle. This means that only a small portion of the object is visible through the aperture.
Examples:
Lens with a NA of 1: The light collects and focuses perfectly onto a small spot at the focal point.
Lens with a NA of 0.5: The light collects and focuses on half of the available light on the object.
Fiber with an acceptance angle of 30°: This means that only 30° of the light entering the fiber is collected and focused on the image plane.
By understanding the numerical aperture and acceptance angle, we can determine the quality of an optical system and how well it can collect and focus light onto a desired target