Question

If the focal length of the eye lens in Ramsden's eyepiece is $f$, then the focal length of the field lens and separation between the field lens and cross wires are respectively :

• A. $3f$ and $f$
• B. $f$ and $f/4$
• C. $3f$ and $2f$
• D. $2f$ and $3f$

Answer 1

The correct option is B $f$ and $f/4$

In Ramsden's eyepiece focal length of eye-piece and field lens is same. so, focal length of field lens is $f$.
separation between field lens and cross wires in Ramsden's eyepiece is $\frac{f}{4}$. Hence correct option is B.