Terminology/Technical Reference
Terminology/Technical Reference
Image sizes
ia
go
na
l:D
There are several types of imaging elements for CCTV cameras, with different
image sizes.
The aspect ratio of CCTV camera is normally 4:3 (H:V).
Imaging element
D
Product symbol
1″
2/3″
1/2″
1/3″
1/4″
Vertical:V
Horizontal:H
Image size(mm)
Horizontal:H Vertical:V Diagonal:D
C
1″
12.8
9.6
16.0
H
2/3″
8.8
6.6
11.0
D, S
1/2″
6.4
4.8
8.0
Y, T
1/3″
4.8
3.6
6.0
Q
1/4″
3.6
2.7
4.5
35mm Camera Lens(Reference)
35mm Film
36.0
24.0
43.3
C/CS-mount
CCTV cameras have either the C-mount or the CS-mount.
Standard
Flange back focal length(mm)
C-mount
CS-mount
17.526 *1
12.5 *1
Diameter of screw thread(mm)
Interchangeability
1-32UNF
C-mount camera
CS-mount camera
C-mount lens
○
○*2
CS-mount lens
×
○
*1 Length in air
*2 Will need a C-mount adapter ring(5mm)when fitting a C-mount lens to a CS-mount camera.
TERMINOLOGY/
TECHNICAL REFERENCE
Focal Length
Flange back and back focal distance
Flange back will be the distance between the
mechanical mount surface and image plane.
Back focal distance will be the distance between the
rear end of the lens part to the image plane.
The focal length will be the distance from the back
principal point to the image plane.
Lower the focal length the wider the image can be
photographed.
Back Principal Point
Image Plane
Image Plane
Focal Length
Back Focus(B.f)
Frange Back(F.f)
J-2
Terminology/Technical Reference
Exit pupil position
Distortion
Distortion is an aberration where the geometric figure of the
object is not reproduced faithfully at the image plane. It is
normally represented by the level shift of an image point from
its ideal position by a percentage of image height or width.
Exit pupil is the image (virtual image) reflected by the lens
located at the back of the lens diaphragm.
Exit pupil position is generally represented with the distance
between the image surface and the exit pupil.
Exit pupil
Barrel Distortion
Image surface
Pin-Cushion
Distortion
Lens
Lens diaphragm
Object
Exit pupil distance
Brightness of a Lens(F and T Numbers)
The F number is an indication of the brightness of lens. The
smaller the value, the brighter the image produced by the lens.
The F number is inversely proportional to the effective diameter
of the lens and directly proportional to the focal length.
F No.= f
d
The scale on the iris ring of lens uses a ratio of 2, because the
value of light incident on a lens is proportional to the cross
section of luminous flux(square of diameter). In other words,
the brightness decreases by half each time the F number is
increased by one F stop.
The F number is a value determined on the assumption that the
transmittance of the lens is 100%. Virtually all lenses however,
have different spectral transmittance, and thus, the same F
number can have different levels of brightness. To eliminate this
inconvenience, a system has been developed to consider both F
number and spectral transmittance, the T number. The T and F
numbers are related to each other as follows:
T No.=
f:Focal length of a lens
d:Effective diameter of a lens
F No.
Transmittance
TERMINOLOGY/
TECHNICAL REFERENCE
MTF(Modulation Transfer Function)
100
MTF(Modulation Transfer Function)represents the
declining contrast rate when shooting a chart consisted of
black and white line width.
MTF %
80
60
40
20
0
Frequency MHz
J-3
× 10
Terminology/Technical Reference
3CCD Camere Lens
100
80
MTF %
Common 3CCD cameras have a ticker glass protection
than a single CCD camera between the lens and the
CCD because three CCDs are placed to correspond with
the red, blue and green color separation.
Therefore, if a lens intended for a single CCD camera is
used on a 3CCD camera, the performance will not be as
high as expected due to the efect on the optics structure
inside of the camera.
Fujinon 3CCD lens are designed to match perfectly with
the common 3CCD cameras in the market today.
The chart shown at the right explains the difference in
MTF when a single CCD lens and a 3CCD lens is put on
the 3CCD camera.
3CCD
60
Single CCD
40
20
0
Center
Diagonal
Image Height
Fixed focal length lens corresponding to megapixel
100
80
MTF %
We have realized a high resolution compact lens
corresponding to mega pixel by adopting the high
technical skills cultivated from broadcast lenses and
optical beam splitters.
The chart shown at the right compares MTF of an
ordinary CCTV lens and a mega pixel corresponding
lens. As the frequency increases, the disparity in MTF
becomes bigger.
60
40
20
0
Frequency MHz
Megapixel Lens
Ordinany Lens
The angle of view is the shooting range that can be
viewed by the lens given a specified image size.
Normally the angle of views is measured assuming a
lens is focused at infinity. The angle of view is obtained
by calculation if the focal length and the image size are
known.
H
θ :Angle of view
Y':Image size
f :Focal length
θ
Image surface
Rear principle point
Example
The angle of view at the side of the image when the
camera size is 1/2" and the focal length is 12.5mm:
θ
θ
Front
principle point
Y':6.4
f :12.5
6.4
θ=2tanー1 =28.72°
2×1 2 . 5
J-4
Image size
Y'
θ=2tanー1 2f
D
TERMINOLOGY/
TECHNICAL REFERENCE
Angle of view
Terminology/Technical Reference
Field of view
If the object distance is limited then the field of view can
be calculated from the following formula.
Y
L
Y=Y'・
f
Y :Objects size
Y' :Image size
L :Distance from lens to object
f :Focal length of the lens
Y′
L
f
Example
The horizontal size where the object can be fully
projected on the monitor when the camera size is 1/2",
the focal length is 12.5mm, and the distance from the
lens to the object is 5m:
Y':6.4
L:5000
f :12.5
5000
Y=6.4× =2560mm
12 . 5
Depth of Field
When focusing on, a certain area in front of and behind
the deep object appears in focus. This area is called the
depth of field. This is because the focus appears in sharp
if the focus misalignment is under a certain quantity. This
certain quantity is called the permissible circle of
confusion.
The depth of field can be calculated by the following formula.
Backward Depth of Field Tr=
δ・F・L 2
f −δ・F・L
Forward Depth of Field
δ・F・L 2
f +δ・F・L
Tf=
2
2
The depth field has following properties.
Depth of field =Tr+Tf
1)The larger F number is, the wider the depth of
field becomes.
Focal Depth =2δ・F
2)The shorter the focal length is, the wider the
depth of field becomes.
f :Focal Distance
F :F number
δ:Permissible Circle
diameter of Confusion
L :Object Distance
3)The longer the distance to the object is, the
depth of field becomes.
4)The backward depth of field is wider than the
forward depth of field.
1"
Permissible Circle of Confusion(mm)
0.04
2/3"
0.028
1/2"
0.02
1/3"
0.015
1/4"
0.011
Tr
Tf
Depth of Field
Focal Depth
J-5
TERMINOLOGY/
TECHNICAL REFERENCE
Image size
Permissible Circle
of Confusion
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