Which optical flaw specifically plagues cheaper or older achromatic refracting telescopes, resulting in a colored halo around bright objects?

Answer

Chromatic aberration

Chromatic aberration occurs in refractors when different colors of light bend at varying angles through the lens, creating a noticeable purple or blue halo surrounding bright targets like the Moon or Jupiter.

Which optical flaw specifically plagues cheaper or older achromatic refracting telescopes, resulting in a colored halo around bright objects?

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