Made colorless or color-corrected; describes a lens system that has been treated to eliminate chromatic aberration; British past tense.
From 'achromatise' + '-ed' (past participle suffix). British spelling variant formed in the 18th-19th centuries as optical science advanced.
An achromatised Victorian telescope from 1850 is still functional today because the glass pairing technique was so clever—it's one of humanity's oldest optical innovations still in everyday use!
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