Angle of view Same as “Field of view” What the camera with a given lens can “see” Horizontal, vertical or diagonal
Lenses - Focal length A small focal length gives wide angle view. A large focal length gives tele view.
Lenses – Calculating the focal length Which focal length is needed for the application? Calculating the focal length (f): f = D*I/ W
Lenses – Depth of field The regions in front of and behind the focus point where the image remains in focus
Lenses - Aperture F number f1.0f1.2f1.4f1.7f2.8f4.0f5.6 % of light passed 20%14.14%10%7.072.5%1.25%0.625%
Lenses – Lens Iris Opening in the lens that controls the amount of incoming light that reaches the image sensor A wire between the camera and the lens is needed with an automatic iris lens.
Lenses - Lens elements A lens contains several lens elements Aspherical elements reduces distortion
Lenses- Mount standards CS-mount ¬ 12.5mm from camera edge to sensor C-mount ¬ 17.5mm from camera edge to sensor ¬ Conversion C to CS is possible
Lenses – Sensor dependency The lens must make an image circle large enough to cover the sensor Larger sensor = more expensive lens The size (e.g. 1/3”) can not be measured anywhere. corresponds to old TV camera tubes Low end lenses produces unsharp corners
Lenses - Resolution A typical CCTV lens has a resolution of 100 lines/mm.
Lenses – Types: Wide angle Large angle of view Good in low light Good depth of field “Barrel” distortion Not for long distances
Lenses – Types: Wide angle image example Example of barrel distortion & missing optical low pass filter
Lenses – Types: Telephoto Good on long distance No barrel distortion Shallow (small ) depth of field Bad in low light
Lenses – Types: Vari-focal The focal length can be adjusted Needs refocusing after focal length adjustment Less precision needed in focal length calculation
Lenses – Types: Zoom Zoom – the focal length can be adjusted with maintained focus Often motorised.
Special Lenses – Fish eye Extremely wide angle (~180 deg) lenses are called “Fish eye lenses”
Lenses – Example: Fisheye image A fish eye lens on a high resolution camera can work as a pan/tilt/zoom camera
Exit pupil is 1-3mm. Can be either low end $1 lenses or high end >$500 lenses. Special Lenses – Pin hole