In a Galilean telescope, which lens is negative in power?

• A. Objective lens
• B. Ocular lens
• C. Eyepiece
• D. Front lens

Answer: (B)

In a Galilean telescope, the eyepiece must be a concave lens to produce a magnified, upright virtual image from the real image formed by the convex objective. A concave lens has negative focal length, i.e., negative optical power, so the ocular lens is the one with negative power. The objective remains a positive lens to collect light and form the intermediate image, while the negative eyepiece allows the eye to view a magnified image comfortable at infinity.