From the reversibility of u and v, as seen from the formula for lens,
It is clear that there are two positions for which there shall be an image on the screen.
Let the first position be when the lens is at O.
Given –u + v = D
=>u = –(D – v)
Placing it in the lens formula
If the object distance is
then the image is at
The distance between the poles for these two object distances is