Which one of the following telescopes contains only mirrors ?

The Newtonian telescope is the correct answer as it is a classic type of reflecting telescope. It was designed by Sir Isaac Newton to eliminate chromatic aberration common in lens-based telescopes. Its primary optical system consists of a concave parabolic primary mirror and a flat diagonal secondary mirror to direct light to the side of the tube.

• Galilean and Keplerian telescopes: These are refracting telescopes that use only lenses (convex and concave) to gather and focus light.
• Schmidt telescope: This is a catadioptric telescope, meaning it uses a combination of mirrors and lenses (specifically a spherical primary mirror and a thin aspherical corrector lens).
• Newtonian telescope: While an eyepiece (lens) is used for viewing, the main light-gathering and focusing mechanism relies entirely on mirrors, distinguishing it from the refracting and catadioptric designs listed.