An equi-convex lens of focal length ' f ' is cut along a diameter,...

An equi-convex lens of focal length ' $f$ ' is cut along a diameter, in two halves (pieces). The two identical pieces of the lens are now arranged as shown in the figure on a common axis at a separation $f$ between the two. The image of an object AB placed at $x=0$ cannot be formed at the distance $x=\xi$ from the object along the axis, for the value of $\xi$ as