CCTV Basics – Lenses

Choosing the Correct Lens

Consider the following parameters:

  • Focal Length

  • Field of View

  • Depth of Field

  • Optical Quality

  • F-stop (aperture) Range

  • Type of Iris Control

  • I.R. Correction in Lens

  • C or CS mount

  • Camera Sensor Format

Focal Length

  • Distance between optical center of the lens and the sensor

  • Determines how much magnification a lens provides

  • Measured in millimeters (e.g. 3.7mm, 9mm, 50mm)

  • Relates directly to the field of view

  • Short focal length provides wide angle of view

  • Long focal length provides telephoto view

Field of View

  • Is the scene width (W), scene height (H) as seen by

        the camera at distance (D) between camera and scene.

  • The following factors determine the focal length

        that must be used to obtain Field of view:

    • Size of the scene to be viewed

    • Distance between the scene and the camera

    • Camera image sensor size

  • Field of view can be calculated with a lens wheel or a calculation program

F-stop (Aperture) Range

  • Lens has a maximum and minimum aperture

        and this specifies the range of light it can suppress

  • Lowest F-stop: iris is fully open

  • Highest F-stop: iris at minimum opening

     

Depth of Field

  • Area within the field of view which appears in focus

     

  • Is influenced by several factors:

    • Wide angle lens has a better Depth of Field than telephoto lens

    • Higher F-stop setting -> better Depth of Field

    • Auto-iris lenses provide optimum Depth of Field

Types of Iris Control

Video-Iris Lens (with built-in electronics)

DC – Iris Lens (No built-in electronics)

Various lenses to choose from

  • Fixed focal length with

    • fixed iris
    • manual iris
    • dc-iris (=passive)
    • auto-iris (=active)
  • Zoom lens with

    • auto-iris
    • manual iris override
  • Manual zoom lens with

    • manual iris
    • auto-iris

Lens and Sensor Relationship

Lens and Sensor Relationship

Lens and Sensor Relationship

Lens and Sensor Relationship

C and CS Mount Lenses

C and CS Mount Lenses

C and CS Mount Lenses

C and CS mount lenses

C and CS mount lenses

What is an IR corrected lens and when do I need that?

IR Corrected Lens and when do I need that?

 

  • Day/Night camera with IR illumination

    • Color image during daylight.

    • Monochrome image is focussed using IR illuminator during night.

       

  • Monochrome camera

    • Image stays in focus using IR illuminators

    • Sharper Dusk/Dawn image because IR light part is focussed.

    • Less car headlamp blooming caused by out of focus IR light

Varifocal lens

    Sample Data Sheet

 

  • 1/3″ CS Varifocal 5 – 50mm

  • High quality optics

  • Manual and DC-iris models

  • DC-iris, 4-pin and 6-pin

  • Compact design

  • f/stop F/1.4

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