What’s “lens”?

“Lens” is the eye of a camera which has a variety of specifications for different needs and environments. For example, indoor surveillance should be aimed at wide-angle image capture while outdoor surveillance such as a parking lot should have the flexibility to have both wide and narrow angles (vari-focal) to get the whole image of the parking lot and be able to see car details.

Lens types

There’re a plenty of lens types used in the CCTV industry: 

  1. Categorized by “focal length”, there are wide angle lenses, mid-range focal length lenses, long-range focal length lenses and vari-focal lenses.
  2. Categorized by “structure”, there are fixed lenses with fixed iris, fixed lenses with manual iris, manual vari-focal lenses, motorized zoom lenses, motorized zoom lenses with auto iris, and motorized zoom lens with motorized focus and iris control.

Requirements & applications for installing camera

  1. Installation requirements:

    1. The front end of the camera (usually the part with the lens) should be 2cm to 4cm lower than the back end of the camera (bracket not included) to prevent glares on the image at the daytime and image overexposure at night caused by receiving too much light directly to the lens.
    2. For installing a IR bullet camera with a 3.6mm lens, the distance between the front end of the sun shield and the lens can’t be over 1.5cm. Otherwise, you might see vague and blurred image with halos around lights at night.
    3. For installing a IR bullet camera with a 6.0mm lens, the distance between the front end of the sun shield and the lens can’t be over 2cm. Otherwise, you might see vague and blurred image with halos around lights at night.
    4. If a part of the image is bright and the other part of the image is dark, and the image is not clear and vague, check the front and two sides of the camera and see if there’s any object to block the IR light reflection.
    5. Halos around lights at night: Check the area where the camera is aiming at and see if max distance where the camera is aiming at is within 3 meters. If yes, please install the camera to where it can see farther than 3 meters or install a camera that its IR projection distance is no more than 30 meters.
    6. Camera purchase tips based on where you want to install:
      1. Office within 20sqm:
        IR cameras with the IR projection distance of up to 30 meters are recommended. If you need to enhance the night vision, you can choose the one with the starlight feature. Please do not use the cameras with the IR projection distance of more than 50 meters because it might cause the video overexposed.
      2. Outdoor use:
        It’s not recommended to use f3.6mm IR cameras with the IR projection distance of up to 30 meters; the one with the IR projection distance of more than 50 meters should be used. If you really need to use f3.6mm IR cameras with the IR projection distance of up to 30 meters, please use the one with the starlight feature.
      3. If the installation environment has sufficient light sources, such as a 24-hour production line, please choose the bullet type camera.

  2. Lens angles and applications:

    1. f2.8mm & f2.5mm wide angle lens (more than 90°), suitable for areas which are not large but need a wider angle of view such as elevators, lobbies.
    2. f3.6mm lens with the angle of more than 60°, suitable for 5m*5m areas
    3. f6.0mm lens with the angle of more than 50°, suitable for areas of 8 ~ 10 meters
    4. f8.0mm lens with the angle of more than 40°, suitable for areas of 20 ~ 30 meters
    5. f12mm & 16mm lens with the angle of more than 30°, suitable for areas of 20 ~ 30 meters
    6. f25.0mm lens with the angle of more than 20°, suitable for areas of 30 ~ 50 meters
    7. Long-range focal length lens with the angle within 20°, suitable for long-distance surveillance
    8. Vari-focal lens, one lens to change the focal length based on the current surveillance area from the wide angle view to narrow angle view, suitable for long-distance surveillance
    9. Pin-hole lens, used for discreet video surveillance

FAQ

There’re a plenty of lens types used in the CCTV industry: 

  1. What’s CCTV?
    CCTV is the abbreviation of Closed Circuit Television, also known as video surveillance.
  2. What’s focal length?
    In optics and photography, the focal length is the distance from the optical center of the lens to the imaging sensor. The focal length is measured in millimeters. For example, f = 8 - 24mm, i.e. the focal length is 8 - 24mm.
  3. How focal length affects viewing angle and image?
    The shorter the focal length, the smaller the image but the wider the viewing angle, and vice versa.
  4. How focal length affects depth of view?
    The shorter the focal length, the deeper the depth of view, and vice versa.
  5. What’s back focal length adjustment?
    When an individual lens is installed, it’s usually required to adjust the back focal length when the focus of the target is lost.
  6. What’s capital F in lens?
    F determines how much light travels through the aperture of a lens. The smaller the value, the more light travels through the aperture and the brighter the image, and vice versa.
  7. What’s aperture?
    “Aperture” works as the iris of the human eye to adjust amounts of light entering the eyes. “F” stands for the diameter of a lens; the smaller the value, the more light travels through the aperture and the brighter the image, and vice versa. For example, the aperture of F2.8 is larger than the aperture of F16.
  8. What’s depth of view?
    “Depth of view” is the range of image sharpness in front of and behind the main subject of a picture. When the range is large, the depth of view is deep and a large zone of the image appears in focus; when the range is small, the depth of view is shallow and a small zone of the image appears in focus.
  9. What’s wide angle lens?
    A wide angle lens is used to capture a wide range in picture because of its short focal length. You can include more items and objects in a picture. When the viewing angle is over 90°, you can take in large areas but image distortion may occur for the close shot.
  10. What’s long range focal length lens?
    A long range focal length lens has the viewing angle within 20° but its focal length can be more than 10mm or 100mm.
  11. What’s vari-focal lens?
    A vari-focal lens allows you to change the focal length of a lens from wide angle to narrow angle; the larger the focal length, the bigger the image but the narrower the viewing angle.
  12. What’s optical zoom? The focal length can be varied physically by moving the lens elements backward and forward to zoom in or zoom out on the image you want to take. The larger the zoom ratio, the farther the image you can take.
  13. What’s video drive lens?
    This lens is capable of automatically adjusting its iris when the light condition is changed, driven by the built-in amplifier to process the video signals sent by the camera and send to the iris motor to change.
  14. What’s direct drive lens?
    This lens uses the DC voltage originated from the camera to adjust its iris when the light condition is changed. No amplifier is used.
  15. What are C-mount and CS-mount?
    “C-mount” and “CS-mount” are the lens mounting types for cameras to be fitted with. The difference between the C-mount and CS-mount lenses is the distance between the flange of the lens and the focal plane of the lens: 17.5mm on a C-mount lens and 12.5mm on a CS-mount lens. A C-mount lens can be used on a CS-mount camera with an adapter ring but a CS-mount lens can’t be used on a C-mount camera.