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

SAGAR SINGH - IIT DELHI
878 Points
13 years ago

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

 Spherical aberration: Inability of a lens to form the point image of a point object on the axis is called Spherical aberration.   In this defect all the rays passing through a lens are not focused at a single point and the image of a point object on the axis is blurred.

All the best.

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