An advantage of refracting telescopes?

• A. Easy to maintain and won't misalign
• B. They require constant realignment
• C. They suffer from chromatic aberration
• D. Can be made to observe extremely large apertures

Answer: (A)

Refracting telescopes use a fixed objective lens to bend light and form an image, so the light path is straightforward and the tube has few moving parts. Because of this, once the telescope is properly assembled, it stays in alignment more easily and requires less ongoing adjustment. That simplicity translates into easy maintenance and a lower chance of misalignment compared with designs that rely on mirrors and frequent realignment. The other ideas come from typical limitations of refractors: realignment needed is more common with systems using mirrors, chromatic aberration is a common drawback of lenses bending different colors by different amounts, and making very large refracting telescopes is impractical due to lens weight and manufacturing challenges. So the best advantage here is the simple, stable optical path that makes maintenance easy and misalignment unlikely.