[HellzStormer]

I'm no expert here. You mention "either side" as if the light came from both the left and the right. But I think the light would be coming along a circle all around the sun depending on exact position.

So the trick here is that if you are at the focus point, you get all that light in a small area "for free". But if you try to catch the light on the way, you now need to catch eveywhere in a whole massive circle, which is basically impossible, so you only catch a minuscule amount of the light. And then have to deal with interferometry.