Post on 22-Dec-2015
. . . 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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