What is the formula for achromatic combination?

B

1

Goto CLZ to know more.

convex lens and

1

concave lens
When a combination of lenses results in no change in focal length of the lens system for different frequencies of light, it is known as achromatic combination of lenses.

For an achromatic combination of lenses, net dispersive power

=

0

i.e

ω

1

f

1

+

ω

2

f

2

=

0

From the conditions of achromatism,
(1)

ω

1

and

ω

2

are positive quantities and

ω

1

&#;

ω

If you want to learn more, please visit our website Achromatic Lenses solution.

Featured content:
The Ultimate Buyer's Guide for Purchasing Aspheric Lens

2

.
and
(2) Focal lengths of the two lenses in contact should have opposite signs.

&#;

we can conclude that options (a) , (c) and (d) are wrong.

So in combination (b), focal length can remain unaffected by variation of focal length with wavelength.

Hence, option (b) is the correct answer.
Why this question?

NOTE: A combination of two lenses which produces net zero dispersion is called an achromatic doublet

The correct option isconvex lens andconcave lensWhen a combination of lenses results in no change in focal length of the lens system for different frequencies of light, it is known as achromatic combination of lenses.For an achromatic combination of lenses, net dispersive poweri.eFrom the conditions of achromatism,(1)andare positive quantities andand(2) Focal lengths of the two lenses in contact should have opposite signs.we can conclude that options (a) , (c) and (d) are wrong.So in combination (b), focal length can remain unaffected by variation of focal length with wavelength.Hence, option (b) is the correct answer.