Why fresnel lens make the image looks bigger???

Answer 1

A Fresnel lens works just the same as a standard convex lens (or any positive lens). The only difference is that a Fresnel lens is flat!

The magnification is related to the focal length of the lens.

Here is a good explanation for calculating the magnification...
http://en.wikipedia.org/wiki/Magnification

Answer 2

A Fresnel lens work more or less has a normal lens in fact, the thing is that its a compressed lens when you make "conceptually" a fresnel lens you take piecies of material that don't really do nothing, your taking away pieces in wich the optical path is multiple of 2pi. in this way you do not nead to have so many material and has it gets very fine you can fit it in a lot of places, bus projectors ..., in plus you do not need the optical presition over a extended circular surface.

In this way the focal lens that you can obtain can be much smaller (one says that the lens has more power). So you can see things much bigger

Answer 3

http://science.howstuffworks.com/question244.htm