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There's a limit to how well sunlight can be focused by a parabolic reflector or a lens because the Sun is not a point source. I wonder if the sunlight could be engineered to work as if it was (much more similar to) a point source.

If almost all of the Solar disc was covered by a coronograph, the light which gets through a small hole would be (almost) a point source. Is that correct?

If then an array of such covered reflectors or lenses concentrated their light to one and the same point, would a better focus be achieved than without covers?

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No, it won't work. After all, it is recommended to make a pinhole camera to watch a solar eclipse. What you suggested is similar to a pinhole camera. Why it won't work, is that the rays that pass through the pinhole are not parallel, but divergent. Light from a point source would have (nearly) parallel rays.

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Good point! But what about two pinhole cameras in a row? Only parallell light beams could pass through both. Would that turn sunlight into a point source? (Or are there other ways to do it?) –  LocalFluff Jun 9 at 13:42
    
@LocalFluff Yes, 2 pinholes in a row should work. You could also mount a lens before the pinhole to produce parallel rays; it would have quite a long focal length. –  LDC3 Jun 10 at 1:20
    
So with such an arrangement, one could use the Sun as an arbitrarily large number of point sources, and thus focus its light at will? –  LocalFluff Jun 10 at 17:51
    
@LocalFluff I don't understand your question. Parallel rays don't focus since there is no convergence. The only way to get many point sources is to have a lot of pin holes. –  LDC3 Jun 10 at 18:25
    
And I don't understand the physics/optics here. But I often read that sunlight cannot be focused well because it isn't a point source (so conversion to microwaves is prefered for transfering the energy, for example). I wonder if many point sources together could be better focused. And if so if the light from the disc of the Sun could be partitioned into many point sources. –  LocalFluff Jun 10 at 18:45

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