Which telescope type has minus powered ocular lens and plus powered objective lens?

Which telescope type has minus powered ocular lens and plus powered objective lens?

• A. Keplerian
• B. Galilean
• C. Newtonian
• D. Cassegrain

Answer: (B)

The key idea is how the powers of the two lenses interact. A Galilean telescope uses a concave eyepiece (negative, minus power) together with a convex objective (positive, plus power). This arrangement makes the light rays diverge after passing through the eyepiece, producing a virtual, magnified image that is upright for the eye to view. In contrast, a Keplerian telescope uses two converging lenses (both plus), which yields an inverted image, and Newtonian and Cassegrain designs rely on mirrors rather than a plus/minus lens pair, so they don’t fit the description of a minus-powered ocular with a plus-powered objective.

The key idea is how the powers of the two lenses interact. A Galilean telescope uses a concave eyepiece (negative, minus power) together with a convex objective (positive, plus power). This arrangement makes the light rays diverge after passing through the eyepiece, producing a virtual, magnified image that is upright for the eye to view.

In contrast, a Keplerian telescope uses two converging lenses (both plus), which yields an inverted image, and Newtonian and Cassegrain designs rely on mirrors rather than a plus/minus lens pair, so they don’t fit the description of a minus-powered ocular with a plus-powered objective.