cross section of a refracting telescope

Magnification depends on the length of the main tube and the size and composition of the lens system.

eyepiece

Lens or system of lenses meant to magnify the image when placed before the eye.

main tube

The barrel of a telescope housing the optical system; light rays travel through the main tube.

objective lens

Lens that captures light from the object observed and causes it to converge.

light

Emitted by a celestial body, light is captured by the objective lens and travels along the main tube until it reaches the eyepiece.