Final answer:
A small field of view results in a less bright image which requires a greater exposure to compensate for the reduced light being captured.
Step-by-step explanation:
When a small field of view is used in optics, such as in microscopy or photography, the image becomes less bright because less light is being captured by the lens or aperture. To compensate for this reduction in brightness, a greater exposure is needed, meaning the film or sensor must be exposed to light for a longer period of time, or a larger aperture must be used to allow more light in. This principle is related to the amount of light that a lens can gather, which is described by its numerical aperture (NA). A lens with a higher NA can gather more light and therefore capture a brighter image. Additionally, the inverse square law applies, indicating that the intensity of light decreases proportionally to the square of the distance from the light source.