“a hole or an opening that primarily limits light propagated through the system”

how aperture works

• optical systems usually have many openings/structures called “stops” that limit light rays
• “aperture stop” is the main stop that controls the cone of light rays that an optical system accepts
• “diaphragms” are usually used to control the aperture stop in cameras
• “f-number” is the ratio of focal length to aperture diameter
• increasing the aperture size (decreasing the f-number) allows more light to reach the sensor
• reducing the aperture size (increasing the f-number) allows less light to reach the sensor
• “depth of field” is the distance between the closest and farthest objects that are in focus in an image
• increasing the aperture size decreases the depth of field
• reducing the aperture size increases the depth of field

  practical uses

• lower f-numbers are better for getting blur around a subject
• higher f-numbers are better for getting everything in focus

  resources

• wikipedia