Draw a labelled ray diagram showing image formation in an astronomical telescope. Derive expression for its magnifying power.

**OR**

Draw a labelled ray diagram showing image formation in a compound microscope. Define its magnifying power and write expression for it.

Question

Draw a labelled ray diagram showing image formation in an astronomical telescope. Derive expression for its magnifying power.

**OR**

Draw a labelled ray diagram showing image formation in a compound microscope. Define its magnifying power and write expression for it.

Accepted Answer

![Figure — Answered alternative asks for a labelled ray diagram of an astronomical telescope; the catalog refracting-tele](/figures/ray-optics-and-optical-instruments/refracting-telescope-fig-9-25.svg)

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> [!TLDR]
> A telescope has a large-focal-length objective forming a real image at its focus, which the small-focal-length eyepiece then magnifies as a simple magnifier; magnifying power (normal adjustment) is $m=-f_o/f_e$.
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> **Construction:** an astronomical (refracting) telescope has two converging lenses — an objective of large focal length $f_o$ and large aperture (to collect more light), and an eyepiece of small focal length $f_e$, arranged with their principal axes coincident.
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> **Ray diagram (normal adjustment — final image at infinity):** parallel rays from a distant object strike the objective and converge to form a real, inverted, diminished image at the objective's focal plane (at distance $f_o$). This image lies exactly at the focal point of the eyepiece too (the two foci coincide, separation $= f_o+f_e$), so the eyepiece receives diverging rays from this image and refracts them into a parallel beam — the final image is virtual, inverted, and at infinity.
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> **Magnifying power:** defined as the ratio of the angle subtended at the eye by the final image ($\beta$) to the angle subtended by the object at the unaided eye ($\alpha$): $m=\beta/\alpha$.
> …

Q.Draw a labelled ray diagram showing image formation in an astronomical telescope. Derive expression for its magnifying power. OR Draw a labelled ray diagram showing image formation in a compound microscope. Define its magnifying power and write expression for it.

Concept understanding — Astronomical Telescope: Refracting and Reflecting

Q.Draw a labelled ray diagram showing image formation in an astronomical telescope. Derive expression for its magnifying power. OR Draw a labelled ray diagram showing image formation in a compound microscope. Define its magnifying power and write expression for it.

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