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Fig. 4.2
Relation between a depth offset
z
and the resulting circles of confusion with radii
c
1
and
c
2
according to Pentland (
1987
)
Fig. 4.3
Dependence of the radius
c
of the circle of confusion on the depth
z
for a lens of
f
2
.
4(
right
). The value of
c
is
given in pixels, where the size of the square pixels corresponds to 4
.
65
=
12 mm at
κ
=
1
.
4(
left
) and for a lens of
f
=
20 mm at
κ
=
m. For each configuration,
the principal distance
b
is assumed to be fixed. The image is best focused at a depth of about 0
.
8m
and 0
.
6 m, respectively
μ
blur. Figure
4.2
reveals that
r/b
b)
with
r
as the lens radius and
c
as the
radius of the circle of confusion, i.e. the circle at which the scene point appears in
the image plane. According to Pentland (
1987
), inserting the third into the second
relation yields
z
=
c/(b
0
−
=
frb
0
/
[
rb
0
−
f(r
+
c)
]
, corresponding to
fb
0
z
=
(4.4)
b
0
−
f
−
2
cκ
with
κ
f/(
2
r)
as the f-stop number of the lens. For illustration, the dependence
of the radius
c
on the depth
z
for fixed focal length
f
and principal distance
b
according to (
4.4
) is shown for a lens of
f
=
=
12 mm at
κ
=
1
.
4 and for a lens of
f
=
20 mm at
κ
=
2
.
4inFig.
4.3
(to allow a comparison with the experimental
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