What optical challenge is inherent to refracting telescopes using an objective lens?
Answer
Chromatic aberration.
Refracting telescopes rely on a large glass lens, the objective lens, to bend or refract incoming light rays to a single focal point. Because different wavelengths (colors) of light travel through glass at slightly different speeds, they bend at slightly different angles during refraction. This differential bending causes the various colors of light to focus at slightly different points along the optical axis. The visible result of this phenomenon is the appearance of colored fringes or halos around bright objects like stars or planets, which is precisely what is defined as chromatic aberration. This issue is a primary limitation that designers must address when building complex refractors.
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