I was using a convex lens and placed the object at principal axis at a distance from optical center lesser than focal length (between $F_1$ and optical center). Then I started observing the size of the image from other side of lens.
At first I had placed my eye close to the $F_2$ and between $F_2$ and $2F_2,$ then moved it away from that towards $2F_2.$ I found that as I moved away from lens, the image was getting bigger and bigger.
That's where my confusion comes in. What I understand is that the size of the image formed at any point is only dependent on its position from lens and lens. It should not be dependent on observer but the size of object seen by observer can get smaller and smaller as he moves away from lens just like a tree when seen from a distance appears small as compared to looking at it from closer distance.
Why is the size of image of object increasing?