CCTV and Video Lens Formulas

Polaris USA CCD Camera Lenses

Part #	Focal Length	field of view	Mount	Cost
IR-MB4	4.3MM	78	C	$45.95
IR-MB6	6MM	54	C	$45.95
IR-MB8	8MM	38	C	$45.95
L1220	12MM	25.7	M12XPO.5	$29.95
L1620	16MM	21	M12XPO.5	$29.95
L2520	2.5MM	153	M12XPO.5	$39.95
L2525	25MM	13.3	M12XPO.5	$29.95
L3520	3.5MM	56	M12XPO.5	$29.95
L4320	4.3MM	78	M12XPO.5	$29.95
L5020	50MM	9.2	M12XPO.5	$39.95
L6020	6MM	54	M12XPO.5	$29.95
L8020	8MM	38.6	M12XPO.5	$29.95



Focal Length	12mm	16mm	25mm
Working Distance	245mm	436mm	681mm
Field of view	98mm	139mm	130mm
Angle of view	22.62 deg.	17.06 deg.	10.96 deg.
Angle of View (manufac)	25.7 deg.	21 deg.	13.3 deg.

FOCAL LENGTH
The focal length of the lens is measured in mm and directly relates to the angle of view that will be achieved. Short focal lengths provide wide angles of view and long focal lengths become telephoto, with narrow angles of view. A "normal" angle of view is similar to what we see with our own eye, and has a relative focal length equal to the pick up device. Our online lens calculator is a simple to use device for estimating focal length, object dimension, and angles of view; alternatively, the FLF-01 View Finder gives an optical way of finding focal length.
CAMERA FORMAT
The size of the camera's imaging device (CCD) also affects the angle of view, with the smaller devices creating narrower angles of view when used on the same lens. The format of the lens, however, is irrelevant to the angle of view, it merely needs to project an image which will cover the device, i.e.: the same format of the camera or larger. This also means that 1/3" cameras can utilize the entire range of lenses from 1/3" to 1", with a 1/3" 8mm lens giving the same angle as a 2/3" 8mm lens. The latter combination also provides increased resolution and picture quality as only the center of the lens is being utilized, where the optics can be ground more accurately.
F STOP
The lens usually has two measurements of F stop or aperture, the maximum aperture (minimum F stop) when the lens is fully open, and the minimum aperture (maximum F stop) just before the lens completely closes. The F stop has a number of effects upon the final image. A low minimum F stop will mean the lens can pass more light in dark conditions, allowing the camera to produce a better image at night. A maximum F stop may be necessary where there is a very high level of light or reflection, as this will prevent the camera from "whiting out", and help maintain a constant video level. All auto iris lenses are supplied with Neutral Density spot filters to increase the maximum F stop. The F stop also directly affects the depth of field.
C or CS MOUNT
Modern cameras and lenses are generally CS mount. With CS mount cameras, both types of lenses can be used, but the C mount lens requires a 5mm ring (Part # ACM-01) to be fitted between the camera and lens to achieve a focused image. With C mount cameras it is not possible to use CS mount lenses.
DEPTH OF FIELD
The depth of field refers to the area within the field of view which is in focus. A large depth of field means that a large percentage of the field of view is in focus, from objects close to the lens often to infinity. A shallow depth of field has only a small section of the field of view in focus. The depth of field is influenced by several factors. A wide angle lens generally has a larger depth of field than a telephoto lens, and a higher F stop setting typically has a larger depth of field than a lower setting. With auto iris lenses, the automatic adjustment of the aperture also means constant variation of depth of field. The small depth of field is most apparent at night when the lens is fully open and the depth of field is at its minimum. Objects that were in focus during the day may become out of focus at night.
AUTO or MANUAL IRIS
Generally we tend to use auto iris lenses externally where there are variations in the lighting levels. Manual iris lenses are used normaly for internal applications where the light level remains constant. However, wIth the introduction of electronic iris cameras it is now possible to use manual iris lenses in varying light conditions and the camera will electronically compensate. There are several considerations to this option though: the setting of the F stop becomes critical; if the iris is opened fully to allow the camera to work at night, the depth of field will be very small and it may be more difficult to achieve sharp focus even during the day. The camera can maintain normal video levels, but it cannot affect the depth of field. If the iris is closed to increase the depth of field, the low light performance of the camera will be reduced.
VIDEO DRIVE or DIRECT DRIVE
With auto iris lenses it is necessary to control the operation of the iris to maintain perfect picture levels. Video driven lenses contain amplifier circuitry to convert the video signal from the camera into iris motor control. With direct drive lenses, the camera must contain the amplifier circuitry, and the lense now only contains the galvanometric iris motor making it less expensive. The deciding factor depends on the auto iris output of the camera. Most now have both types.

Subtechnique's Navitar Page
All Video Lenses are Not Created Equal
Navitar and Fujinon video lenses are the benchmark against which all CCTV lenses
should be measured. Quality construction, coupled with precision engineering, result
in video optics that are sharp, high resolution and optically precise.
We offer a complete range of video lenses for every industrial application. Video lenses
from Navitar are the ideal choice for applications ranging from PC board inspection to
viewing glass bottles on a production line.
Video Lens Selection
There are a growing number of video imaging applications in which a single, constant
magnification factor and a fixed working distance are required in order to maximize
contrast and performance. Navitar has responded to this need with a wide range of
fixed focal length lenses.
To determine which lens will work best for your application, please review the information
in this catalog or feel free to call one of our engineers. Determining all the necessary
parameters for video lens selection including focal length, field of view and camera chip
size, need not be a mysterious or intimidating process. The following information will help
you to select the lens that’s exactly right for your firm’s application.
Understanding Focal Length and F/Number
Video lenses can be classified into three categories according to focal length: standard,
wide angle and telephoto. Focal length is the distance between the camera sensor and
the center of the lens. The greater the focal length, the larger the image will appear.
Therefore, the greater the focal length, the more the lens becomes telephoto in application.
Standard Lens
A standard lens doesn’t change the size of the object being viewed.
Wide Angle Lens
A wide angle lens provides a wider field of view and therefore a smaller image of the object
being viewed than the standard lens.
Telephoto Lens
A telephoto lens produces a larger image of a distant object. The longer the focal length,
the larger the object will appear.
The f/number is the measurement of the ratio between the focal length and the diameter
of the entrance pupil (where the light enters the lens). The smaller the f/number, the larger
the opening and the faster the lens (or more light the lens will transmit). The f/number
determines the amount of reflected light reaching the camera sensor.
How to Determine the Lens Focal Length Your Application Requires:
To choose the proper lens for a particular application, the following factors must be considered:
·    The size of the area to be imaged (field of view).
·    Distance from the camera sensor to the object or area under surveillance.* (Be sure to
include the flange distance.)
·    The size of the camera’s image sensor device.
·    You must be consistant. If you are measuring the width of your object, then use the
horizontal CCD specifications, etc. If you are working in inches, then do your
calculations in inches and convert to millimeters at the end.
*Please do not confuse working distance with object to image distance. Working distance is
measured from the front of the lens to the object being viewed. Object to image distance is
measured from the CCD sensor to the object. To calculate the lens focal length required,
you must use the object to image distance
FL = Oject to Image Distance
(M + 2+ 1/M)
Magnification = Object Size
Image Size
(size of CCD Chip)
Consider this example: You have a 1/2” C-mount CCD Camera (6.4mm horizontal). There
is a 12” distance between the object and the CCD sensor. The object size is 2.5”. The
conversion factor is 1” = 25.4mm.
Image Size
The ratio of the length of the horizontal to vertical sides of a video image is called
the aspect ratio, which is normally 4:3 (H:V) for standard video.
Image Sensor     Image Circle    Horizontal    Vertical
1/3”    Ø 6.0mm    4.8mm     3.6mm
1/2”    Ø 8.0mm    6.4mm    4.8mm
2/3”    Ø 11.0mm    8.8mm    6.6mm
1”    Ø 16.0mm    12.8mm    9.6mm

Relationship Between Angle of View & Image Sensor Size
An important factor to remember is that cameras with different image sensor chip sizes
(such as 1/3”, 1/2”, 2/3” and 1”), using the same focal length lens, will each yield a
different field of view. Lenses designed for a larger image sensor device will work on a
new, smaller size camera. However, if a lens designed for a smaller format image sensor
device (such as 1/3”) is placed on a larger one (such as 2/3”), the image on the monitor
will have dark corners.
Image sensor sizes are in a ratio of 1:0.69:0.5:0.38. This means that 1/2” format is 50%
of 1” format, 1/2” format is 75% of 2/3” format and 1/3” format is 75% of 1/2” format.

Camera to Monitor Magnification
Monitor Sizes (diagonal) in inches.
Camera Format    9”    12”    13”    20”    27”
1/3”    38.1X    50.7X    55.0X    84.6X    114.1X
1/2”    28.6X    31.8X    41.3X    63.5X    85.7X
2/3”    20.8X    27.7X    30.0X    46.2X    62.3X
1”    14.3X    19.1X     20.6X    31.8X    42.9X
Minimum Object Distance (M.O.D.)
Minimum object distance (M.O.D.) indicates how close the lens can be placed near the object
for shooting. It is measured from the vertex of the front glass of the lens.

Flange Distance & Back Focal Length
Flange Distance
Distance between mechanical mount surface and the image sensor.
C-MOUNT    17.526mm    (.690”)    (in air)
CS-MOUNT    12.5mm    (.492”)    (in air)
Back Focal Length
Distance between vertex of the rear element lens and image sensor.

C-Mount & CS-Mount Compatibility
     C-Mount Camera     CS-Mount Camera
C-Mount Lens     OK    OK
CS-Mount Lens     NO     OK

Focal Length
Parallel incident light transmitted into a convex lens converges
to a point on the optical axis. This point is the focal point of the
lens. The distance between the principal point in the optical
system and the focal point is referred to as the focal length. For
a single thin lens, the focal length is equal to the distance between
the center of the lens and the focal point.

Angle of View & Field of View
The angle of view is the shooting range that can be viewed by the lens given a specified image size. It is
usually expressed in degrees. Normally the angle of view is measured assuming a lens is focused at infinity.
The angle of view can be calculated if the focal length and image size are known.

If the distance of the object is finite, the angle of view is determined as follows: tan 1/2 q = H'/2(f+f/m), where
m=object size/sensor size.

Zoom Ratio
Zoom ratio is the ratio of the focal length at the telephoto end to that at the wide end. A zoom lens can change
the size of an object appearing on the monitor to the extent specified by the zoom ratio.
Navitar General Lens Formulas
Focal Length    EFL = OI/(M + 2 + 1/m)
Object to Image Distance    OI = [EFL x (1+m)2 ]/mOI = m(EFL) + (EFL+VOA+BF) + EFL/mVOA = Vertex to Vertex Lens Length
Object to Lens Distance    OL = EFL + EFL(m)
Lens to Image Distance    LI = EFL + EFL/m
(Approximate distance to the nodal points: EF + EFL(m) to the front vertex.)
    F# = 1/(2NA) F# = EFL /Entrance Pupil DiameterNA = 1/2F# NA = Sinø/2
Effective F/#    Eff. F/# = F/# (m+1)
Clear Aperture (Minimum)    Aperture = FL/(F/#)
Depth of Focus    DoF = 0.00002/NA2 (in inches)DoF = 0.0005/NA2 (in mm)
Conversion Factors
1 Inch = 25.4 Millimeters
1 Meter = 39.37 Inches
1 Micron = 0.001 Millimeter
1 Degree = P/180 Radians
1 Degree= 0.0174533 Radians
1 Micron (µ) = 1,000 Nanometers (nm)
1 Micron (µ) = 10,000 Angstroms (Å)

General Lens Formulas . . . . . . . . . .

Focal Length
FL = CCD x WD/FoV

Magnification
m = Image Size/Object Size

Object to Image Distance
OI = [FL x (1+m)2 ]/m
OI = m(FL) + (FL+VOA+BF) + FL/m
VOA = Vertex to Vertex Lens Length

Object to Lens Distance
OL = FL + FL(m)

Lens to Image Distance
LI = FL + FL/m
(Approximate distance to the nodal points: FL + FL(m) to the front vertex.)

F/# = 1/(2NA)
F/# = FL /Entrance Pupil Diameter
NA = 1/2 F/#
NA = Sin q/2

Effective F/#
Eff. F/# = F/# (m+1)

Clear Aperture (Minimum)
Aperture = FL/(F/#)

Depth of Focus
DoF = 0.00002/NA2 (in inches)
DoF= 0.0005/NA2 (in mm)

Conversion Factors
1 Inch = 25.4 Millimeters
1 Meter = 39.37 Inches
1 Micron = 0.001 Millimeter
1 Degree = P/180 Radians
1 Degree = 0.0174533 Radians
1 Micron (µ) = 1,000 Nanometers (nm) 1 Micron (µ) = 10,000 Angstroms (Å)

General Lens Formulas . . . . . . . . . .

How to Determine the Lens Focal Length Required

Optical Characteristics of Video Lenses

Relationship Between Angle of View and Image Sensor Size . . .
An important factor to remember is that cameras with different image sensor chip sizes (such as 1/4", 1/3", 1/2", 2/3" and 1"), using the same focal length lens, will each yield a different field of view.

Camera to Monitor Magnification

Minimum Object Distance . . . . . . . . .
Minimum object distance (M.O.D.) indicates how close the lens can be placed to the object for shooting. It is measured from the vertex of the front glass of the lens.

	CCD PC Board Lens Information & Calculations


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General Lens Formulas . . . . . . . . . .

How to Determine the Lens Focal Length Required

Optical Characteristics of Video Lenses

Relationship Between Angle of View and Image Sensor Size . . . An important factor to remember is that cameras with different image sensor chip sizes (such as 1/4", 1/3", 1/2", 2/3" and 1"), using the same focal length lens, will each yield a different field of view.

Camera to Monitor Magnification

Minimum Object Distance . . . . . . . . . Minimum object distance (M.O.D.) indicates how close the lens can be placed to the object for shooting. It is measured from the vertex of the front glass of the lens.

Relationship Between Angle of View and Image Sensor Size . . .
An important factor to remember is that cameras with different image sensor chip sizes (such as 1/4", 1/3", 1/2", 2/3" and 1"), using the same focal length lens, will each yield a different field of view.

Minimum Object Distance . . . . . . . . .
Minimum object distance (M.O.D.) indicates how close the lens can be placed to the object for shooting. It is measured from the vertex of the front glass of the lens.