[mabbo]

They wouldn't though.

The Lagrange points are stable positions relative to two bodies, like the earth and the moon or the earth and the sun. But those things are moving, orbiting. The points move with them. The line from the earth to any Lagrange point won't stay stably pointing at any star in the sky.

And even then, the focal point of this atmospheric lens is at a specific distance that is not, afaik, the distance to any Lagrange point.