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#telescope design

2 public questions tagged with this topic.

Optical Instruments - Simple and Compound Microscope

Why does the image in a reflecting telescope remain free of chromatic aberration?

**Compound microscope** M = m_o × M_e, objective magnification m_o = v_o/u_o ≈ L/f_o, L tube length, eyepiece M_e = 1+D/f_e (image at D) or D/f_e (infinity). Objective forms real inverted magnified image at focal plane of eyepiece, eyepiece acts as simple microscope magnifying it. A reflecting telescope uses mirrors instead of lenses as the objective. Mirrors reflect all wavelengths of light uniformly, avoiding the wavelength-dependent refraction that causes chromatic aberration in lenses, resulting in a clearer, color-corrected image. Substituting values gives Due to uniform reflection of all

Ref: NCERT > Physics Book > Ray Optics > Optical Instruments - Simple and Compound Microscope

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Thin Lenses - Lens Formula, Magnification and Power

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

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