Leica DM R Serie Mode D'emploi page 49

®
PL FLUOTAR , HC PL FLUOTAR,
HCX PL FLUOTAR
Semi-apochromats with a field performance of
at least 25 mm. The improvement in field
performance and colour correction compared
with the achromats is particularly important for
photomicrography.
PL APO, HC PL APO, HCX PL APO
Plan apochromats with a field performance of
over 25 mm, the best objectives in the Leica
range.
PLAN L, N PLAN L
Achromats with particularly long free working
distances, specified in the Leica objective
charts. L objectives with apertures over 0.25 are
designed for use without a coverglass. Field
performance over 20 mm.
PLAN H
Achromats for use with heating stages which
have a 1.80 mm thick quartz window and with
interference attachments. Field performance
over 20 mm,
e.g. 10x/0.25 PH 1.
10x
Magnification of the objective, which is also
indicated by colour of the lower edge of the
objective collar (see chart).
0.25
Numerical ap erture of the objective, derived from
the angular aperture of the ray cone penetrating
the objective. The aperture influences a number
of image factors and is therefore just as
important as the magnification. It influences:
resolution, which also depends on the wave-
length λ of the light. A general rule for a medium
wavelength λ = 0.55 µm for visible light is:
λ
resolution = –––– = –––––
2 n.A
Example: aperture 0.50
resolution (opt.) = 0.55 : 1.0 = 0.5 µm
Dep th of field (axial resolution)
Image intensity: This increases quadratically
with the aperture, so objectives with high
apertures, especially immersion objectives, are
preferred for fluorescence microscopy, for
example.
Coverglass sensitivity (cf 1st line 0.17!)
1.25 – 0.65
Objective with built-in iris diaphragm to adjust
the aperture (41.3), e.g. for darkfield immersion.
Attention:
Objective with built-in diaphragm!
The knurled may only be used for adjusting
the diaphragm, not for screwing the objective
in or out.
Risk of damage!
0.55
2 n.A
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