What happens if a camera lens is too small for the image sensor?

When a camera lens is too small for the image sensor, it results in vignetting, which is characterized by an uneven distribution of light across the image. Specifically, this phenomenon is observed as black corners or a significant drop in brightness around the edges of the image. This occurs because the lens cannot gather enough light to illuminate the entire sensor evenly, leading to darkened areas in the corners while the center of the image may appear properly exposed.

This situation can be more pronounced in wide-angle lenses or with sensors that have a larger than normal size compared to the lens. The effect can affect the overall composition of the image and might necessitate cropping or adjusting the image in post-processing to achieve a balanced appearance. Understanding the relationship between lens size and sensor dimensions is essential for achieving optimal photographic results.