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Low Mag Video Lenses
Flange Distance
Distance between mechanical
mount surface and the image
sensor (in air).
C-Mount=17.526 mm / .690”
CS-Mount=12.526 mm / .493”
Back Focal Length
Distance between vertex of the rear
element lens and image sensor.
C-Mount and CS-Mount Lens
Compatibility
When using a C-mount lens for a
CS-mount camera, a C/CS-mount
adapter (5 mm thick) is required
between the lens and the camera.
Angle of View
and Field of View
The angle of view is the shoot-
ing 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 is not used. In-
stead, the dimension of the range
that can actually be shot, or the
field of view, is used.
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 prin-
ciple 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 cen-
ter of the lens and the focal point.
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.
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 ver-
tex.)
F/# = 1/(2NA)
F/# = FL /Entrance Pupil Diameter
NA = 1/2 F/#
NA = Sin
θ
/2
Effective F/#
Eff. F/# = F/# (m+1)
Clear Aperture (Minimum)
Aperture = FL/(F/#)
Depth of Focus
DoF = 0.00002/NA
2
(in inches)
DoF= 0.0005/NA
2
(in mm)
Conversion Factors
1 Inch = 25.4 Millimeters
1 Meter = 39.37 Inches
1 Micron = 0.001 Millimeter
1 Degree =
Π
/180 Radians
1 Degree = 0.0174533 Radians
1 Micron (
μ
) = 1,000 Nanometers (nm)
1 Micron (
μ
) = 10,000 Angstroms (Å)
C-Mount and CS-Mount Lenses
Flange Distance and
Back Focal Length
Field of View
Angle of View
Focal Length
C-Mount and CS-Mount Lens/
Camera Compatibility
Compatibility
C-Mount
Camera
CS-Mount
Camera
C-Mount Lens
OK
OK
(w/ adapter)
CS-Mount Lens
NO
OK
