Glossary
1)Total magnification
Total magnification = Eyepiece’s magnification X objective’s magnification
2)Numerical aperture (N.A.)
N.A. value will affect resolution and image’s brightness, it is the leading parameter for
objectives. N.A.= n X sina
n stands for refractive index of the medium between objective and specimen or condenser (air
or oil immersion)
a stands for half angle of max. aperture angle in the axis
The image will be sharper and brighter when the N.A. value is bigger
3)Resolution
Resolution can be measured by the distance value from one point to another one which could
be distinguished on the object surface
Resolution=λ /(2XN.A.)
λstands for wavelength ( λ= 0.55um)
4)Working distance
The distance between the object surface to the first surface of optical system when you get
the sharpest image. The W.D. will become more short when the magnification for the
objective is bigger.
5)Eyepiece view field
The max diameter measured when the diaphragm is open. 10X/18 means the magnification is
10X and the max diameter of view field is 18mm
6)Effective view field
Liner view field which is observed on the object surface
Effective view field = eyepiece view field / objective’s magnification
7)Depth of field
Depth of field stands for depth of the space in which there is sharp image on the object surface.
Depth of field will be longer when the diaphragm reduces. Depth of field will be shorter when
the N.A. becomes bigger.
IV. Configuration