Reduces the amount of light Light diffraction limits the how small an aperture can be. Light has wave-like properties. This is evident when you place an aperture in the path of a light source. Instead of a single pinpoint of light, there is a bright central disk surrounded by a diffuse ring of light. This image is called an airy disc .
Light diffraction is the reason that an exact image of a specimen is never achieved .
In work done by Sir George Airy and Ernst Abbe in the 19th century the following equation was established to calculate the limit of resolution. This is also called the half-aperture angle. The formula then becomes easier. Under this equation, the smaller the wavelength of light the greater the resolution. In addition the larger the numerical aperture the greater the resolution.