Mohan obtained a sharp inverted image of a distant tree on the screen placed behind the lens. He then moved the screen and tried to look through the lens in the direction of the object. He would see:

A convex lens forms a real and inverted image of a distant object (at infinity) at its principal focus ($F$). A screen is used to capture and display this real image. However, the presence of the screen is not a prerequisite for the image to exist in space; the refracted light rays still converge and intersect at the focal plane. When the screen is removed and Mohan looks through the lens from behind the focus, his eye intercepts these diverging rays coming from the focal plane. As a result, he sees a real, inverted image of the tree suspended in the air at the focus of the lens.