Chapter 3 Individual Operations
101
Individual
Operations
8
Adjusting the Aperture Diaphragm
The aperture diaphragm is used to adjust the illumination
angular aperture, and is important as it affects the resolution,
contrast, focal depth, and brightness of an optical image.
With a motorized condenser, operating the DIA aperture
diaphragm button changes the size of the aperture diaphragm
from diameter 2.0 mm up to 30.6 mm.
Press the left side (
mark side) of the DIA aperture diaphragm
button to open, and the right side ( mark side) to close the
diaphragm.
Operation on DS-L3 (See “23.2 Controlling the Microscope”.)
ND
8
ND
32
OUT
IN
NCB
11
Adjusting the aperture diaphragm
PA__2x____Z:_____0.000um
BF____AS17.9mm__FS30.0mm
Proper size of the aperture diaphragm
Normally, 70 to 80% of the numerical aperture of the
objective is the proper size. It provides satisfactory
images with suitable contrast. Since an excessively small
aperture diaphragm opening will degrade image
resolution, Nikon does not recommend setting the
aperture diaphragm to less than 60% of the numerical
aperture of the objective.
A small aperture diaphragm opening reduces resolution
and brightness but increases contrast and depth of focus.
On the contrary, a large aperture diaphragm size
increases resolution and brightness but reduces contrast
and depth of focus. These characteristics involve inherent
tradeoffs and cannot be optimized independently.
Proper size of the aperture diaphragm
Calculating the aperture diaphragm diameter
Use the following formula to determine the suitable size o
the aperture diaphragm.
34xNAx ratio
NA: Numerical aperture of objective
(Indicated on the side of the objective.)
Ratio: 0.70 for 70％, 0.80 for 80%
<Example>
Using Plan 40x objective
Numerical aperture: 0.75
In this case, to set the aperture diaphragm of the
condenser to 70%,
34 x 0.75 x 0.70 = 17.85 (mm)
Rounded to one decimal place, 17.9 (mm) are calculated.
40x / 0.75
Plan 40x
Nikon JAPAN
/ -WD
Plan 40X
40x / 0.75
/ -WD
Indication for 40x magnification /
numerical aperture 0.75
Proper numerical aperture: 34 x 0.75 x 0.70=17.85
Relationship of the aperture diaphragm size with the optical image's state
Aperture diaphragm Resolution Brightness Contrast Focal depth
Stop down Lower Darker Larger Deeper
Open Higher Brighter Lesser Shallower
Aperture diaphragm's adjustment timing
Be sure to adjust the aperture diaphragm each time you change the objective.
Interlocked operation of the aperture diaphragm
The adjustment of the aperture diaphragm size can be interlocked with switching of objectives. See “19.2 Interlocking
Function” for conditions for interlocking and interlocked operations.
DIA aperture diaphragm button
perture
diaphragm image
Pupil of objective
70～80
100
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