Coronagraph...
Hi Alberto
As RL has rightly noted the Focus is about ~ 600 AU away. The Sun is 1/360,000 th of its luminosity and its disk is < 3" of arc which wouldn't be hard to cover over with a suitably placed coronagraph. Because the light brought to the focus is from such an immense area the Sun is kind of like the missing bit of a primary mirror through which the focussed light passes in a Cassegrain telescope and so shouldn't be too much of a problem.
Adam