Cassegrain reflecting telescopeकैसेग्रेन परावर्ती दूरदर्शकCassegrain reflecting telescope

NCERT Fig 9.26 · Class 12 Physics · Chapter 9 · interactive diagram

Parts and what they mean

• Principal axis (मुख्य अक्ष) —
• Concave primary mirror (objective) (अवतल प्राथमिक दर्पण (अभिदृश्यक)) — Large mirror with a hole in the centre. A mirror has no chromatic aberration, is lighter than a lens of the same quality and can be supported over its whole back.
• Convex secondary mirror (उत्तल द्वितीयक दर्पण) — Intercepts the converging light before the primary focus and sends it back through the hole.
• Telescope tube (दूरदर्शक की नली) — Short tube, yet the effective focal length is large.
• Light from a distant star (दूर के तारे से प्रकाश) — Arrives as parallel rays.
• Converging towards the primary focus (प्राथमिक फोकस की ओर अभिसरण) — Would meet at F (dashed) if the secondary were absent.
• Reflected by the secondary (द्वितीयक से परावर्तित) — Pass through the hole and focus behind the primary, where the eyepiece is placed.
• Eyepiece (नेत्रिका) — Observer sits behind the primary instead of inside the tube.
• Eye (आँख) —
• Focus of the primary (प्राथमिक का फोकस) —
• Final focus (अंतिम फोकस) — Behind the hole in the primary.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 9.26. Report a mistake