ABSTRACT
After focusing the sample, we can define the working distance as the gap between the front plane of the objective lens and the sample surface, as seen in Fig. 21.2.
Figure 21.2 Concept of working distance. 21.2.4 Total MagnificationWhen we observe the image through the binocular, we have the total magnification (M) as M = M(ob) × M(oc) (21.5)where M(ob) and M(oc) are the magnification of the objective lens and the eyepiece, respectively. 21.2.5 Numerical Aperture
The numerical aperture (NA) is written as
NA = n sin q (21.6)where n is the refractive index of the surroundings of the objective lenses and the sample (i.e., n = 1.0 for air and n = 1.5 for oil) and θ is (1/2) radiation angle from the front of the objective lens.
