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Anupam Dalmia Grade: 10

What are defects of lens????

spherical abrasion and chromatic abration

7 years ago

Answers : (1)

879 Points

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

Lens Defects



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.

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All the best.

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Askiitians Expert

Sagar Singh

B.Tech, IIT Delhi

7 years ago
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