In photography, bokeh is the way a lens renders out-of-focus points of light. The shape of bokeh depends on the shape of the lens’s aperture more than the out-of-focus objects themselves.

Flat-Earthers fail to take properly-focused photos of stars and planets because of their lack of photography skills and because their cameras are not suitable for the purpose. They are just getting bokeh, which tells us more about their equipment (and lack of knowledge) than the actual intended objects.

A different camera lens can produce a different shape of bokeh. Concentric circles (onion rings, shooting targets) usually result from aspherical lens elements. Polygonal shapes are due to the outlines of the lens’s aperture when stopped down. Donut-shaped bokeh is due to the obstruction by the secondary mirror in a mirror lens. The cat’s eye bokeh is caused by the cylindrical shape of the lens when the object is near the edge of the frame. The bokeh shape tells us more about the camera and lens than the intended objects.

Flat-Earthers invented wild assumptions to explain why stars and planets do not appear as they are supposed. The real explanation is more straightforward: these shapes are just bokeh, and they tell us more about their photography skills or the lack thereof.