(a) A refracting telescope has f_o = 120 cm, f_e = 1.5 cm. Find M and the tube length (normal adjustment). (b) How much more light does its 8 cm objective gather than the naked eye (pupil 6 mm)? (c) A Newtonian reflector has a 20 cm f/8 mirror. Find its focal length and M with a 10 mm eyepiece. Step 1: M = −f_o/f_e = −120/1.5 = −80× (inverted). Normal adjustment (final image at infinity): tube length = f_o + f_e = 121.5 cm. Step 2: Light grasp ∝ area ∝ D²: (80/6)² = (13.33)² ≈ 178×. Stars ~5.6 magnitudes fainter become visible — the real reason telescopes beat eyes. Step 3: f/8 means f_o = 8 × 20 cm = 160 cm. M = −160/1.0 = −160× with the 10 mm eyepiece. Same formula as the refractor — only the objective's nature (mirror vs lens) changed.