User`s manual

Preliminary
96 • Technical Specifications Genie Monochrome Series-GigE Vision Camera
Lens Modeling
Any lens surrounded by air can be modeled for camera purposes using three primary points: the first
and second principal points and the second focal point. The primary points for a lens should be
available from the lens data sheet or from the lens manufacturer. Primed quantities denote
characteristics of the image side of the lens. That is, h is the object height and h
′ is the image height.
The focal point is the point at which the image of an infinitely distant object is brought to focus. The
effective focal length (f
′ ) is the distance from the second principal point to the second focal point. The
back focal length (BFL) is the distance from the image side of the lens surface to the second focal
point. The object distance (OD) is the distance from the first principal point to the object.
Primary Points in a Lens System
Magnification and Resolution
The magnification of a lens is the ratio of the image size to the object size:
h
h
m
'
=
Where m is the magnification, h’ is the image
height (pixel size) and h is the object height
(desired object resolution size).
By similar triangles, the magnification is alternatively given by:
OD
f
m
'
=
These equations can be combined to give their most useful form:
OD
f
h
h ''
=
This is the governing equation for many
object and image plane parameters.