DIAGRAMS SHOWING RELATION BETWEEN ANGULAR APERTURE AND RESOLUTION

Peter Gray, Handbook of Basic Microtechnique, Third Ed., McGraw-Hill, 1964

Fig 1-9 shows the concave mirror of a freshman-type microscope (Fig 2-1) casting a narrow cone of light into the objective. This cone has a total angle of 64 degrees so that the numerical aperture is 0.6. Fig. 1-10 shows a substage condenser used to increase the angular cone to 96 degrees. Since the system is working in air (i = 1), the numerical aperture is 0.8. Fig. 1-11 shows both the substage condenser and the objective oiled to the slide. The angle of the cone is 116 degreesm, and i, for the oil, = 1.56. The N.A. is thus 1.3. The relation between N.A. and resolution is explained in the text.