This is an interactive tutorial on the topic of magnification. A lens is bi-convex if both surfaces are convex. In this Java simulation, users move a virtual bi-convex lens toward and away from an object to observe changes in the size of the image produced by the lens. The accompanying text tutorial gives detailed information about the geometric principles governing the situation. This item is part of a larger Microscopy Primer developed by the National High Magnetic Field at Florida State University. SEE RELATED ITEMS on this page for a link to the complete primer.