The opening in a lens to adjust the light inflow within the camera is known as the Aperture or Iris. Its working is similar to the human eye's pupil. The more light enters the lens, the brighter the image will be.
Opaque blades, known as the diaphragm, cover the aperture and adjust its opening depending on the camera settings. The measuring unit for an aperture is called f/stop or focal stop. There can be multiple f/stops in a camera lens. Fixed, manual, and auto Iris lenses are available for different applications.
Fixed iris cameras can be used in environments with fairly consistent fixed light. The manual iris can be adjusted by turning a ring based on light availability, whereas the auto iris, normally conrolled by the camera, adjusts automatically depending on the light.
A large aperture means more light can get into the camera lens. It is also termed “low-ranging” because of the lower f/stop values (f/1.4 to f/4). Also, at lower f/stop values, the exposure time required to achieve a properly exposed image is shorter.
Conversely, the small aperture means a little opening is available for the light to enter the camera. The f/stop values, in this case, are often in the f/16 to f/22 range. With larger f/stop values, the exposure time required to achieve a properly exposed image is longer. They are also known as "slow apertures."
Also, the aperture is essential in determining the proportion of the image's sharpness. The larger aperture means the area of the image in focus will be much sharper, while the background of your picture will be less focused and blurred (shallow depth of field).
Similarly, a smaller aperture will result in an even focus for the image's background and foreground (higher depth of field). However, the overall focus of the image will have less sharpness as compared to a lens with larger aperture.
In most CCTV Cameras, the apertures are usually fixed. It reduces the device's complexity and keeps costs low. A larger aperture must be chosen to get clear footage in low light or nighttime, whereas a smaller aperture suits perfectly well in a highly lit situation.
A slight decrease in the f-stop value for the dim light situations can reduce motion blur and provide less grainy footage.