Anulus
A mass that is never drawn bends the light behind it, and once a loop it lines up with a galaxy and the galaxy closes into a ring.
The mass is never shown. Only what it does to the light behind it.
A dark sky of stars and faint nebula, and in front of it a mass that is not drawn. Light passing near it is bent. The stars around the empty place stretch into short arcs on a circle, and inside the circle the sky is squeezed small. No pixel in the frame is coloured by the mass itself.
The mass drifts round a circle and once per loop passes exactly in front of one galaxy. The galaxy bends into an arc, splits into two arcs on opposite sides of the empty place, and at 7.5 seconds closes into a ring, blue-white and beaded with pink where its knots are. Then it opens again.
The lens adds no colour and no light. It only moves light that was already there.
Rendered offline from a single closed-form shader by the same module code a live page would run. No camera, and nothing leaves the machine.