chandler wrote: > > When you hold a magnifying glass just above the newspaper, it forms an > image you can most certainly see, that is just below the actual surface > of the newspaper. Not wanting to confuse things more, but... If that magnifying lens is a) convex (as they usually are!) and b) more than 1 focal length from the newspaper then a) the image it produces is a *real* one b) that image is located on the opposite side of the lens to the object A real image is formed when rays of light from a point on the object pass through the lens and converge at some point on the other side of the lens. If you put a piece of paper there, you'll see an image. A normal camera lens forms real images. A virtual image is formed where rays of light passing through a lens deviate in such a manner as to appear to be coming from a point (this is a slack definition, but allows me to move a little further). Using this definition, a piece of flat glass, air, or even a vacuum suffices. becuase rays of light coming from an object appear to be coming from it (perhaps because they do :-) A negative lens will cause these rays to diverge, and thus appear to be coming from a different location. Clearly these rays will mot converge, so there's nowhere you can place a piece of paper to see an image cast on it. A teleconverter is a good example of a negative lens that photographers probably have lying around. compare what you get with a normal lens and a teleconverter when, in a darkened room, you place them alternatly between a bright object (say a TV) and a piece of paper. One will form a small image of the TV, the other won't. But you can look through them and see the TV. Our eye, has a positive lens, and this allows these diverging rays to be converged back to a point, thus forming a *real* image which we perceive as vision. Steve
