Final answer:
Axial resolution refers to the ability of an optical system to distinguish between two points along the same line of sight and is calculated using the Rayleigh criterion formula θ = 1.22 λ/D.
Step-by-step explanation:
The formula to calculate axial resolution can be derived from the Rayleigh criterion, which provides a method to determine the smallest possible angular separation between two point sources that can still be distinguished as separate entities. According to the Rayleigh criterion, the axial resolution can be expressed using the formula θ = 1.22 λ/D, where θ is the minimum resolvable angle (in radians), λ is the wavelength of light used, and D is the diameter of the aperture through which the light is passing. In the context of a microscope or a telescope, this formula helps determine the best obtainable resolution, which is crucial in observing fine details in biological specimens or distant celestial bodies. The smaller the result of this formula, the higher the resolution of the optical system, allowing for more detailed images.