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Focal lengths of two lenses are f and f'...

Focal lengths of two lenses are f and f' and dispersive powers of their materials are `omega` and `omega'`. To form achromatic combination from these, which relation is correct ?

A

f' = 2f

B

f' = -2f

C

f' = f/2

D

f' = -f/2

Text Solution

Verified by Experts

The correct Answer is:
B
For achromatic combination
`f/(f.)= omega/(omega.)`
but `omega/(omega.) = omega_0/(2omega_o) = 1/2`
`-f/(f.) = 1/2 or f. = -2f`
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