Aperture and shutter speed control the amount of light that passes from the lens to the film or digital sensor of a camera. Aperture is the size of the opening within the lens. The lower the f-stop number (1.4 for example) the larger the opening and the more light is passed through. Shutter speed is closely related. It is the amount of time that the lens is open. The combination of the size of the opening in the lens and the amount of time that the lens is open determine the exposure.

High shutter speed and fast lens/Big open aperture.

Underexposure without a change of lighting corresponding to your aperture.

The ratio of the velocity of light in a vacuum to that in a medium is the refractive index of a lens.

It is represented by n = c/v, where n = refractive index , v = characteristic speed and c = speed of light 299792 kmsec-1 or 1 Planck speed.

Light perception and storage speed。