PerkinElmer Optoelectronics
10
5.1.1 Estimating the Working Distance
The following relationships assume a thin lens relationship that is deemed
sufficiently accurate to permit reasonably accurate estimates of the optical
configuration. Referring to Figure 5:
f
AF
EXT
ID
+
+
=
WD
ID
X
AL
M
=
=
1
*
+
=
M
M
WD
f
M
M
f
WD
)
1
(
*
+
=
Where: ID = Image Distance
EXT = Length of Extender
AF = Sensor to Camera Face distance
f = focal length of lens
AL = Length of sensor array
X = Web with imaged
M = magnification
WD = working distance
Since the actual results will vary from these idealized estimates, sufficient
adjustment capability is required.
Example
Assuming that an 80 mm lens has been chosen for an LC30XX camera and is
installed without an extender and that it is desired to image a 36” (882 mm) web.
The following calculations result in the working distance estimate:
5
.
85
80
8
.
5
=
+
=
mm
mm
ID
065
.
0
882
3
.
57
=
=
=
mm
mm
X
AL
M
The estimated working distance then is:
)
"
8
.
51
(
4
.
1315
065
.
5
.
85
mm
mm
M
ID
WD
=
=
=
