Axio Imager 2 INSTRUMENT DESCRIPTION ZEISS
Objectives
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2.5 Objectives
The objectives are the optical heart of the
microscope. They may be labeled as follows:
N-ACHROPLAN 20x/0.45 ∞/0.17.
where
20x : Objective magnification, with a
defined color ring on the objective
allocated to each magnification step
(ZEISS color code)
0.45 : Numerical aperture
∞ : Infinite image distance; these
objectives can only be used with ICS microscopes from Carl Zeiss.
0.17 : Can only be used with cover slip thickness D = 0.17 mm.
or
− : Can be used with cover slip thickness D = 0 or 0.17 mm.
Other labels:
Oil : Oil immersion objective
Ph 2 : Phase-contrast objective with green inscription and phase stop Ph 2
The color of the inscription denotes the contrasting method the objective is designed for:
Black: Standard
Green: Phase contrast
red: Strain-free for polarization (Pol); low-strain for differential interference contrast
(DIC)
The color rings indicate the magnification of the objective (color code):
Color ring on
objective
Black Brown Red Orange Yellow Green Light
blue
Dark
blue
White
Magnification
factor
1x; 1.25x 2.5x 4x; 5x 6.3x 10x
25x; 32x
40x; 50x 63x 100x;
150x
Objective magnification multiplied by eyepiece magnification (usually 10x) yields overall visual
magnification: e.g. 10 x 10 = 100x.
When working with the microscopes, total magnification should not be above or below the range of
useful magnification. The range of useful magnification is defined by Ernst ABBE as 500 to 1,000 times
the numerical aperture of the objective used. The human eye cannot resolve any details beyond this.
Accordingly, the range of useful magnification for an objective with a numerical aperture of 0.3 is
between 150x and 300x.
The higher the numerical aperture of the objective, the greater the necessity for exact observance of the
cover slip thickness of 0.17 mm. For this reason, certain objectives are equipped with a correction mount
for adjustment to different cover slip thicknesses. To this end, a specimen area should be searched for,
and the position of the correction ring where optimum focus and image contrast are obtained
determined (refocusing is invariably required).
Fig. 8 Objective
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