Lens Modeling; Magnification And Resolution - Dalsa 4M30 User Manual

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750, which does not include a mounting ring, and the CORION™ HR-750 series hot
mirror.

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
The focal point is the point at which the image of an infinitely distant object is brought to
focus. The effective focal length (f
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.
Figure 19: 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:
m
By similar triangles, the magnification is alternatively given by:
m
These equations can be combined to give their most useful form:
h
h
Example: An acquisition system has a 512 x 512 element, 10μm pixel pitch area scan camera,
a lens with an effective focal length of 45 mm, and requires that 100μm in the object space
correspond to each pixel in the image sensor. Using the preceding equation, the object
distance must be 450 mm (0.450 m).
10
100
03-032-20044-01
'
where m is the magnification, h' is the image height
h
=
(pixel size) and h is the object height (desired object
h
resolution size).
'
f
=
OD
' '
This is the governing equation for many object and
f
=
image plane parameters.
OD
μ
m 45 mm
= =
OD 450
μ
m OD
'
is the image height.
'
) is the distance from the second principal point to the
mm ( . 0 450 m )
Falcon 4M Camera Manual
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