II
1
Combinations of 10x Eyepiece with CFI P Objectives
Objective
Magnification
Total
Magnification
Numerical
Aperture
Real Viewfield*
Depth of
Focus
Resolving
Power
Working
Distance
4× 40× 0.1 5.5 mm(5 mm)
63.2
µ
m 2.8
µ
m
30 mm
10× 100× 0.25 2.2 mm(2 mm)
10.1
µ
m 1.1
µ
m
6.1 mm
40× 400× 0.65 0.55 mm(0.5mm)
1.2
µ
m 0.4
µ
m
0.65 mm
100× 1000× 1.25 0.22 mm(0.2 mm)
0.4
µ
m 0.2
µ
m
0.18 mm
2
Microscope Terminology
(1) Total Magnification
The total magnification of a microscope is the individual magnifying power of the
objective multiplied by that of the eyepiece.
(2) Numerical aperture (N.A.)
The numerical aperture is an important factor in determining the efficiency of the
condenser and objective. It is represented by the formula:
N.A. = n sin α
where n is the refractive index of the medium (air, immersion oil, etc.) between the
objective lens and the specimen or condenser, and α is half of the maximum angle at
which light enters or leaves the lens from or to a focused object point on the optical
axis.
(3) Resolving Power
The ability of an optical system to discriminate between two discrete objects
separated by a minute distance. The more minute the distance, the higher the
resolving power of the optical system. In relation to the numerical aperture,
the resolving power is represented by the following formula:
Resolving power =
..2 ΑΝ×
λ
where λ is the used wavelength of light. (The resolving power in the above table is
indicated for λ = 0.55 µm.)
(4) Working Distance (W.D.)
The clearance between the front of the objective and the upper surface of the
coverglass, when a specimen image is sharply focused. Generally, the higher the
magnifying power of the objective, the shorter the working distance.
(5) Field Number of the Eyepiece
The diameter of the opening of the fieldstop inside the eyepiece measured in mm.
When an eyepiece has an indication of “10x / 22”, it means that the magnification is
10x and the field number is 22 for that eyepiece.
(6) Real Viewfield
The diameter in mm of the field of view observable through the eyepiece.
Real viewfield = field number of eyepiece / magnification of objective
* The figures in the parenthesis are for eyepieces of field no. 20.
The figures out of the brackets are for eyepieces of field no. 22.
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