Magnification depends on the length of the main tube and the power of the eyepiece.
See cross section of a reflecting telescope in : french | spanish
eyepiece
Lens or system of lenses meant to magnify the image when placed before the eye.
light
Emitted by a celestial body, it crosses the main tube and is sent back by the concave primary mirror; the secondary mirror intercepts it and directs it toward the eyepiece.
