Which aberration occurs when light is focused at different areas of the film plane or sensor?

The phenomenon being described is best identified as coma. This type of optical aberration occurs when off-axis light rays are focused in a way that causes points of light to appear distorted and shaped somewhat like a comet, hence the name "coma." It is particularly noticeable with bright points of light in the corners of the image and results in a blur or streaking effect.

In photography, coma affects the sharpness and clarity of images, especially in wide-angle lenses. When light from the edges of a scene fails to converge at the same point as light from the center, it produces this distinct distortion, making it evident at the periphery of the frame.

Chromatic aberration, on the other hand, results from different wavelengths of light being focused at slightly different points, leading to color fringing rather than a focus issue across the film plane or sensor. Barrel distortion and pincushion distortion are types of geometric distortions that occur when straight lines are curved inwards or outwards, respectively, but they do not specifically relate to the focusing of light across different areas of the sensor in the way that coma does.