. . . 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

Compression CPU

Flashmemory

DRAM

EthernetInterface

Camerafunctions

Lens Optical filter Image sensor

Lens and optical filter in a camera

Filters - IR filter

Filters the Infrared light invisible for the human eye but visible for cameras

Transmission curve (Example)

20

0

40

60

80

100

300 400 500 600 700 800 900 1000 1100

I/RVisible light

IRRadar TV Sound Radio

Radio WavesYRays

XRays

UV

300 400 500 600 700 800 900

Wavelength

Wavelength in nanonmetres

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

Focal length

IrisMountLens

element

Angle of view

Same as “Field of view” What the camera with a given lens can “see” Horizontal, vertical or diagonal

Horizontal Angle ofView (HOV)

Vertical Angle of View(VOV)

Lenses - Focal length

A small focal length gives wide angle view. A large focal length gives tele view.

Focal point

Focal length

Lenses – Calculating the focal length

Which focal length is needed for the application?

Calculating the focal length (f): f = D*I/ W

D f

I

Lenses – Depth of field

The regions in front of and behind the focus point where the image remains in focus

Focus point

Lenses - Aperture

F number

f1.0 f1.2 f1.4 f1.7 f2.8 f4.0 f5.6

% of light passed

20% 14.14% 10% 7.07 2.5% 1.25% 0.625%

F2

F5.6

F16

00

5'1.5m

10'3m

15'4.5m

20'6m

25'7.5m 8

8

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

Spherical lens element

Image plane

Aspherical lens element

Image plane

Lenses- Mount standards

C-mount Lens

17.526 mm

CS-mount Lens

12.5 mm

5 mm spacer

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

Horizontal

Vertical

Image Size

Image Circle

Image Size 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.

1611864.5

1"

1/4" 1/3" 1/2"2/3"

1"1/4" 1/3" 1/2" 2/3"

Lenses – Types: Wide angle

Focal point

Short focal length

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

Focal point

Long focal length

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 adjustedwith 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

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