ABSTRACT
The numerical apertura (N.A.) depends on the angular aperture (CY.) of the lens and [he refractive index (n) of the medium between the lens and the specimen:
N.A. == n sine (1I2a) where "a" is the angular aperture of the lens and "n" is the refractive indc'" of the medium (air, saline solution, immersion au) interposed between the 1..:'15 and the specimen.
