What size lens would to need to seperate a planet orbiting a star?

If the star was 20 light years away from you, and the planet orbited its star at a distance of 5.2 AU?What size lens would to need to seperate a planet orbiting a star?(5.2 AU/20 ly) is about 0.85 arcseconds (if I calculated right). So according to this article (http://en.wikipedia.org/wiki/Dawes'_limi鈥?/a> ), it would take a lens (or a mirror) of only about 5.4 inches diameter.



But that doesn't mean you can see it. Planets are millions of times dimmer than their stars.What size lens would to need to seperate a planet orbiting a star?Rick B is correct. I would just add that it might be possible to image the planet if you could maneuver a space telescope into a position where the star (but not the planet) is occulted by a distant asteroid or perhaps by Pluto. The occultation would have to last long enough for the telescope to gather enough light from the planet, and that would require a much larger aperture. You could improve the resolution considerably by having several telescopes spread apart, but it would be more difficult to keep them in the zone of occultation all at the same time.