Question

A terrestrial telescope is made by introducing an erecting lens of focal length, $f$, between the objective and eyepiece lens of an astronomical telescope. This causes the length of telescope tube to increase by an amount equal to

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

Answer 1

The correct option is D $4f$

Since, the mInimum distance between the real object and real image is $4f$.

Therefore length of telescope increase by $4f$.