This simulation allows the determination of the focal length of a converging lens by determining the position of the real image that can be viewed only when projected onto the screen. The object (red arrow) is fixed at zero position; its height and orientation, however, can be modified. There are 4 converging lens options each with a different focal length. The simulation only allows the visualization of real images. The lens can be moved between the object and the screen. To do this, just click on the center of the lens and drag it to the desired position. The real image will only be shown when the screen is located at the position where the image is formed. The screen can be moved from the right end to the lens position; to do this click on the X point in its upper left corner of the screen and drag. In some situations, the image can be viewed in a range of screen positions. In this case consider the center of the range as the correct position of the image.