finding focal point of concave lens using concave and convex lenses

Question

I was doing this experiment. Let's look at this image:

Suppose we get the imaginary object at dv by convergence lens. And this object is like a real object for the concave lens. Then how do we get a real object on the screen? It is known that only virtual objects can be made on the screen by convex lenses, and the image should be before the real object and after the lens.

According to TLE (Thin lens equation) we can find the focal point, however i'm confused about what is real and imaginary here.

Also, I had tried hard to draw ray diagram for this one. No success in forming an imaginary image in dv or real image at dr.

Answer 1

If the concave lens was not there and the object was at a distance greater that its focal length the convex lens would form a real image.

Introducing a concave lens results in the incoming rays from the convex lens being refracted as shown in the diagram above.
The refracted rays are still convergent and so form an image $I$ at a distance $q_2$, your $d_v$, from the the concave lens.
After passing through the convex lens where the rays would have met is at a distance $p_2$, your $d_R$, from the concave lens and that can be thought of as a virtual object for the concave lens.