What are defects of lens????spherical abrasion and chromatic abration

Dear student,

Lens Defects

Chromatic aberration: Image of a white object is coloured and blurred because µ (hence f) of lens is different for different colours. This defect is called chromatic aberration.   µv > µR so fR > fV   Mathematically chromatic aberration = fR – fv = ωfy   ω = Dispersive power of lens.   fy = Focal length for mean colour √fRfv

Removal: To remove this defect i.e. for Achromatism we use two or more lenses in contact in place of single lens.

Mathematically condition of Achromatism is : ω₁/f₁ + ω₂/f₂ = 0

or     ω₁f₂ = –ω₂f₁

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