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A 10 mm chrome ball bearing makes a great artificial star - put it out in the sun for daytime use (position it in the sun against a dark background), or put it down the far end of a dark hallway and shine a bright halogen light on it for indoor / night testing.
When you do the maths, the image of the sun or a halogen light on a 10 mm sphere at a distance of 20 metres or so is small enough to be a pinpoint for practical optical testing purposes.
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