Which of the following is NOT an advantage of a reflecting telescope, such as that used by Isaac Newton?

• A. It reduces chromatic aberration because it uses mirrors
• B. It can be built with very large apertures
• C. It avoids refraction in Earth's atmosphere
• D. Reflector telescopes are much heavier and need to be made much smaller than refracting telescopes

Answer: (D)

Reflecting telescopes use mirrors instead of lenses, so they don’t suffer from chromatic aberration where colors focus at different points. This design also allows for very large apertures because mirrors can be supported from behind and made in large sizes more readily than thick lenses. Since there’s no refracting element in the light path, the instrument avoids those kinds of optical distortions, and the optical tube can be kept relatively compact compared to long refractors. The statement about being much heavier and needing to be much smaller is not correct—mirrors enable large, lightweight apertures, and the tubes can be quite long or short depending on the design.