Final answer:
The disadvantage of refractors compared to reflectors is that they suffer from chromatic aberration. This is because different wavelengths of light do not focus at the same spot, causing the image to be blurred or fringed with color. Reflecting telescopes avoid this problem and are generally preferred for larger telescope designs.
Step-by-step explanation:
The disadvantage of a refracting telescope (refractor) when compared to a reflecting telescope (reflector) of the same size is that refractors do not focus all wavelengths in the same place, leading to chromatic aberration. This chromatic aberration occurs because different wavelengths of light are bent, or refracted, by different amounts as they pass through the lens material. This means that each color comes into focus at a slightly different point, which can cause the image to appear blurry or fringed with color.
Reflecting telescopes, which use mirrors instead of lenses, do not suffer from this problem because mirrors reflect all wavelengths at the same angle, thus avoiding chromatic aberration. Moreover, reflections do not require the light to pass through the material, so imperfections within the glass of the mirrors are generally less problematic for the image quality. Reflecting telescopes are also typically easier and less expensive to construct at large sizes since they require only one precision-polished surface, and the mirror can be supported from behind, making them more durable and less sensitive to gravitational deformations.