Refracting (astronomical) telescopeअपवर्ती (खगोलीय) दूरदर्शकRefracting (astronomical) telescope

NCERT Fig 9.25 · Class 12 Physics · Chapter 9 · interactive diagram

Parts and what they mean

• Principal axis (मुख्य अक्ष) —
• Objective (large fo, large aperture) (अभिदृश्यक (बड़ी fo, बड़ा द्वारक)) — Collects light from the distant object and forms a real image at its second focal point. A wider objective gathers more light and resolves finer detail.
• Eyepiece (small fe) (नेत्रिका (कम fe)) — Magnifies that image; final image inverted (at infinity for normal adjustment).
• Parallel rays from a distant object (दूर की वस्तु से समांतर किरणें) — They arrive at a small angle α to the axis.
• Emergent parallel rays (निर्गत समांतर किरणें) — Leave the eyepiece at the larger angle β.
• Real intermediate image h (वास्तविक मध्यवर्ती प्रतिबिंब h) — At the common focus; h = fo tan α.
• Angle α (कोण α) — Angle subtended by the object at the objective (or eye).
• Angle β (कोण β) — Angle subtended by the final image at the eye. m = β/α ≈ (h/fe)/(h/fo) = fo/fe.
• Common focus (उभयनिष्ठ फोकस) — Second focus of the objective coincides with the first focus of the eyepiece (normal adjustment).
• fo (fo) — Focal length of the objective.
• fe (fe) — Focal length of the eyepiece.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 9.25. Report a mistake