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CCTV Video Lenses

CCTV Lens Accessories   /  Back to main 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.

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.

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.

Back Focal Length
Distance between vertex of the rear element lens and image sensor.

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

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)