Question

If ${}^{\prime }{f}^{\prime }$ is focal length of lens in Ramsden's eye piece, cross wires are placed at:

• A. $\frac{f}{3}$ distance behind the field lens
• B. $\frac{f}{3}$ distance in front of the field lens
• C. $\frac{f}{4}$ distance in front of the field lens
• D. $\frac{f}{4}$ distance behind field lens

Answer 1

The correct option is C $\frac{f}{4}$ distance in front of the field lens

If ${}^{\prime }{f}^{\prime }$ is focal length of lens in Ramsden's eye piece, than the cross wires are placed at $\frac{f}{4}$ in front of the field lens.