I don't use primary optics which are not made by myself.
18 How long does it take to travel 36 light years with tolerable acceleration and deceleration? Sep 14 '11
17 Why can I never see any stars in the night sky? Apr 26 '12
15 Why can't you escape a black hole? Dec 15 '11
14 Please explain the physics of a Cloud Chamber Sep 13 '11
13 Could there be a body of water the size of a planet? Sep 19 '11
12 Can you damage your eyes viewing Venus? Mar 12 '12
11 Is it possible to see satellites with the naked eye? Mar 7 '12