I performed a simple experiment to find the focal length of a magnifying glass. Taking a white sheet of paper as a screen and a building as object at infinity, i got a clear image at 12.5 cm, which is approximately the focal length of the lens. Plugging this into the formula for magnifying power of a simple microscope, we get the maximum and minimum powers as 3 and 2. However the carton says the magnifying glass is 5x. Plugging into the formula we get focal length 5 cm, and when a tried it, i couldnt get an image at all. So what is wrong? The formula i used for power of simple microscope was 25 divided by f for minimum power and 1 plus 25 divided by f for maximum power.