... M A K E S Y O U R N E T W O R K S M A R T E R Lenses & Filters

Lens and optical filter in a camera

Filters - IR filter  Filters the Infrared light invisible for the human eye but visible for cameras

Filters - Optical low pass filter  Splits the incoming light  Improves color representation

Filters – Example: Without optical low pass filter

Filters – Example: With optical low pass filter

The Lens

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% %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

Questions & Answers