People strive hard to make the most perfect mirror they can.
They optimize the telescope with cooling fans, baffles, secondary mirror optimization and offset. In most cases, yes. Eyepieces are magnifying lenses that allow the observer to scrutinize the image that the telescope has created and is holding in the air just in front of the eyepiece. The magnification of a telescope depends on the telescope s focal length and the eyepiece s focal length. The quotient of the two gives you your magnification, or power.