... MAKES
YOUR
NETWORK
SMARTER
Lenses & Filters
Lens and optical filter in a camera
Flash
memory
Camera
functions
Compression
CPU
DRAM
Lens
Optical filter
Image sensor
Ethernet
Interface
Filters - IR filter
100
Wavelength
Y
Rays
Radio Waves
X
Rays
UV
IR
Radar
TV
80
Sound Radio
60
Visible light
I/R
40
20
300
400
500
600
700
800
Wavelength in nanonmetres
 Filters
900
0
300
400
500
600
700
800
Transmission curve (Example)
the Infrared light invisible for the
human eye but visible for cameras
900
1000
1100
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
Wid
ng
a
e
ew
i
v
of
le (
)
f view)
o
le
g
n
a
o
t
Tele(pho
Mount
Iris
Lens
element
Angle of view
Horizontal Angle of
View (HOV)
 Same
as “Field of view”
 What the camera with a given lens can “see”
 Horizontal, vertical or diagonal
Vertical Angle of View
(VOV)
Lenses - Focal length
Focal point
Focal length
 A small
focal length gives wide angle view.
 A large focal length gives tele view.
Lenses – Calculating the focal length
W
I
D
f
Calculating the focal length (f): f = D*I/ W
 Which
focal length is needed for the
application?
Lenses – Depth of field
Focus point
Dep
 The
th o
f fie
ld
regions in front of and behind the focus
point where the image remains in focus
0
0
5'
1.5m
10'
3m
15'
4.5m
20'
6m
8 8
Lenses - Aperture
25'
7.5m
F2
F5.6
F16
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%
Lenses – Lens Iris
A wire between the camera and the lens
is needed with an automatic iris lens.
 Opening
in the lens that controls the amount of
incoming light that reaches the image sensor
Lenses - Lens elements
Spherical lens element
Image plane
 A lens
contains
several lens elements
 Aspherical elements
reduces distortion
Aspherical lens element
Image plane
Lenses- Mount standards
17.526 mm
12.5 mm
5 mm spacer
C-mount Lens

CS-mount
¬ 12.5mm from camera edge to sensor

C-mount
¬ 17.5mm from camera edge to sensor
¬ Conversion C to CS is possible
CS-mount Lens
Lenses – Sensor dependency
Image Size
Image Circle

Image Size

Vertical


Horizontal
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
1/4"
1/3"
4.5
6
8
11
1/2"
2/3"
1/4"

2/3"
1/2"
1/3"
A typical CCTV lens has a resolution of 100 lines/mm.
1"
16
1"
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
– the focal length can be adjusted
with maintained focus
 Often motorised.
 Zoom
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
Special Lenses – Pin hole

Exit pupil is 1-3mm.
 Can be either low end $1 lenses or high end
>$500 lenses.
Questions & Answers
2
3
YZ
XYZ
395
X Y ZK D
HU
P
PO
15 PQ
10.000
PQ
O
YZ KH D
O