In a reflecting telescope, why is a concave mirror preferred over a convex lens as the objective?
**Lens formula** 1/f = 1/v - 1/u, f focal length (m), u object distance, v image distance, sign: u negative if object left of lens in Cartesian convention, magnification m = v/u, real image inverted m negative, virtual erect m positive. Power P = 1/f (diopters D), f in meters, +5 D means f=0.2 m=20 cm converging. A concave mirror avoids chromatic aberration (color distortion) that occurs in lenses due to different wavelengths refracting differently. Mirrors reflect all wavelengths uniformly, providing clearer images, and are easier to support mechanically for large apertures, enhancing light-g
Ref: NCERT > Physics Book > Ray Optics > Thin Lenses - Lens Formula, Magnification and Power