Film sensitivity is primarily due to different sizes of what component?

Film sensitivity is primarily determined by the size and distribution of silver halide crystals within the emulsion layer of the film. Sensitive films contain various sizes of these crystals, which respond to light differently. Larger crystals are generally more sensitive to light, resulting in faster film speeds, while smaller crystals produce finer grain but require more light to achieve the same exposure. This interplay influences the film's ability to capture images in varying lighting conditions and directly affects the overall sensitivity of the film.

While grain particles are related to the size of the individual crystals, they are a byproduct of the development process rather than the source of sensitivity. Color filters and aperture openings play important roles in the photographic process but do not influence the intrinsic sensitivity of the film itself.