4M Stop Action Camera Manual
PRELIMINARY
49
750, which does not include a mounting ring, and the CORION™ HR-750 series hot
mirror.
g three primary
the lens data sheet or from the lens
side of the lens. That
bject is brought to
′
)
is the distance from the second principal point to the
ack 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 21: Primary Points in a Lens System
Lens Modeling
Any lens surrounded by air can be modeled for camera purposes usin
points: the first and second principal points and the second focal point. The primary
points for a lens should be available from
manufacturer. Primed quantities denote characteristics of the image
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 o
focus. The
effective focal length (f
b
second focal point. The
n
The magnification of a lens is the ratio of the image size to the object size:
Magnification and Resolutio
m
h
=
′
where m is the magnification,
(pixel size) and h is the object height (desired object
h
h’ is the image height
resolution size).
By similar triangles, the magnification is alternatively given by:
m
f
OD
=
′
These equations can be combined to give their most useful form:
′
=
′
h
h
f
OD
This is the governing equation for many object and
image plane parameters.
Example:
An acquisition system has a 512 x 512 element, 10
µ
m pixel pitch area scan camera,
a lens with an effective focal length of 45mm, and requires that 100
µ
correspond to each pixel in the image sensor. Using the preceding equation, the object
distance must be 450mm (0.450m).
m in the object space
10
100
45
450
0 450
µ
µ
m
m
mm
OD
OD
mm
m
=
=
( .
)
DALSA 03-32-10121-09
