Why is the focal point of a convex lens real and that of a concave lens virtual?

Question

Why is the focal point of a convex lens real and that of a concave lens virtual?

Answer 1

A convex lens actually focuses the light to a point (like a magnifying glass)

A concave lens spreads the light out, so the focal point would be behind the lens, on the side that the light is coming from. The light isn't actually focused at that point because it hasn't passed through the lens yet.  Look at this picture:  http://upload.wikimedia.org/wikipedia/co...