Filter
Top Products
3
Objective Numerical
Aperture
(NA)
Color
ring
Coverglass (c.g.)
thickness
Position for auxiliary
condensor lens
N Plan 2.5x 0.07 Brown Any/without c.g. off
N Plan 5x 0.12 Red Any/without c.g. off
N Plan 10x 0.25 Yellow Any/without c.g. on
N Plan 20x 0.4 Green 0.17 mm on
N Plan 40x 0.65 Blue 0.17 mm on
C Plan 63x 0.75 Black 0.17 mm on
Table 1. Objectives in Leica DM LB
N Plan stands for planachromat and C Plan for achromat objectives. The achromatic
objectives are corrected for axial chromatic aberration in two wavelengths (blue and
red; about 486 and 656 nanometers, respectively). Furthermore, achromatic objectives
are corrected for spherical aberration for the green color (546 nanometers). If focus is
chosen in the green region of the spectrum, images will have a reddish-magenta halo.
Achromatic objectives yield their best results with light passed through a green filter.
Planachromat is a flat-field corrected achromat objective, which corrects the field
curvature.
NA indicates the numerical aperture of an objective. This determines the resolving
power of the objective. The higher the NA, the better the resolution. None of the
objectives are to be used with immersion oil.
For wider illumination when using 2.5x and 5x objectives, move the auxiliary
condensor lens out of the light path by swinging the rod connected to the lens (Figure
4).
Figure 4. Auxiliary condenser lens switch
2.5 Focusing
Focus on the sample by turning either of the focusing wheels located identically on
both sides of the microscope (Figure 5). Focusing raises or lowers the specimen stage;
the outer wheel is for coarse focusing, and the inner one for fine focus adjustment.