
69-16 Medical, Biomedical, and Health
sensing element causing it to produce an alternative signal every time at least one of the images crosses
th
e
se
nsing
el
ement
. By co
mbining
mu
ltiple
fa
cets,
it is po
ssible
to sh
ape
an
y
de
sirable
de
tecting
pa
ttern
in th
e
e
ld
of vi
ew,
in bo
th
ho
rizontal
an
d
ve
rtical
pl
anes
. Po
sitioning
of th
e
fa
cet
le
ns,
fo
cal
di
stances,
nu
mber,
an
d
a pi
tch
of th
e
fa
cets
(a di
stance
be
tween
th
e
opt
ical
ax
es
of tw
o
ad
jacent
fa
cets)
ma
y
be
ca
lculated
in ev
ery
ca
se
by ap
plying
ru
les
of ge
ometrical
opt
ics
. e fo
llowing
pr
actical
fo
rmulas
ma
y
be a
pplied
to
nd
t
he
f
ocal
l
ength
o
f
a f
acet:
f
Ld
=
∆
(69.11)
and the facet pitch (a di ...