V. MANIPULATION
OF EACH ELEIV]ENT
6) Use of
Field Diaphragm
The fie d diaphragm s used for determlning lhe
i
um
nated area on
the
spec
men The
s
ze
of
the
dlaphragm
is adlusted by manip! at
ng
thefeddaphragmcontro rng. Stoppinq down the
diaphraqm to
such an extent that the circqrfglelcc
qtlh€
lllulll
q
circumscribes
or
inscribes that
oJ
the evepiece field ol
y!€tq
s
recommended for
genefal
microscopy f a w der area
than requ red
s
luminated,
extraneouslLghtw
lentefthef edofvew, caus
ngflafe
n the image and owerng the coftrast Therefore,
especaly n
pholom
crography, the
proper
adl!rstrnent
of the {eld d aphragm
s
very lmpofiant Generaly,
good
resu ts w ll be achleved
when the
d aphragm s stopped down io such an extentthatthe
d ameterofthe
luminated
area
is
s
ightly
afger
than the d agonal of the
f m format
7) Use of Condenser Aperture
Diaphragm
The condenser aperlure dlaphragm
is
provided
for adjust ng the
fumerica ape{Lrfe
(N
A.)of
the !l
!m
nating system oi lhe
,-.
,
-
t6..Tm
ne5 ere o
.,
o
,.i"
image. contrasl, depth offocus. and brghtness.
Stopp
ng
down
the
aped!re
diaphragm w ll ower the
resolut on and
bfghtnessbLrt ncrease the contrast and depth oflocus.
Ingenera.
when lt is stopped down to 70% to
80%
of
the numerical ape4llq
of the obiective, a
good
lmage of appropf ate
contrast w I be
obtained
(F
g.
l 1
)
To
adlLrst
the
s
ze
of
the
condensef
aperture d aphragm,
man
pu
ate
thedaphragm contro ring reierrng to thc condenser's
N.A. scae.
orafterremovngtheeyepiecelfom
theeyepecetube, adl!stthesze
of
the d aphfagm,
observ
ng the image of the diaphragm
that s
vis b e of the br
ght
c fcle of the ex l
pupilon
the ins de ofthe objective
Slopping down the apenure diaphragm
too tar w I o\/er the
reso v ng
power
Therefore, it ls recommended not lo slop
down the
aperture to a s ze sma ler than 60% of lhe
N
A oftheobjectve
n
,6
6, 60
.ho,
oo
o,.
gor-lo
11
Size oithe condenser
aperture diephr.gm
20
Fi9
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