You must click on this link to begin: Start Me.
The object (the arrow), its image and the principal rays can be moved by clicking & draging the top of the arrow shaped object in the animation.

• With respect to the starting configuration, find the focal length.
• Now move the object so that its inverted image has the same height. Find the focal length now.
• Move the object so that p = f . Do you see an image? Click on this link to replace the object with a Point source.
• Restore the object and move it so that p < f . Is there a real or virtual image? Is the image height smaller or larger than that of the object? What is the sign of q?