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Congratulation David on a really superb piece of engineering.
Regarding diffraction spikes I have heard anecdotally that another way to suppress them is to insulate the vanes with royal black velvet. The thermal boundary layer you get on the surface of bare metal vanes actually creates an optical thickness much thicker than their mechanical dimension. The insulation while thickening the mechanical profile reduces the optical profile by removing the thermal boundary layer.
Another approach is to use a curved spider milled out of solid aluminium.
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