if you put the camera/dector/eyepiece at the focus of a reflecting teleschope, it will block light going into the mirror. How can we get around that problem to make good reflecting telescopes

The electric field between square plates of a parallel-plate capacitor has magnitude e. the potential across the plates is maintained with constant voltage by a battery as they are pulled apart to twice their original separation, which is small compared to the dimensions of the plates. the magnitude of the electric field between the plates is now equal to a)e b)e/4 c)e/2 d)4e e)2e