Heisenberg's Uncertainty Principle is one of the important basic principles of quantum mechanics. In most of the books on quantum mechanics, this uncertainty principle is generally illustrated with the help of a gamma ray microscope, wherein neither the image formation criterion nor the lens properties are taken into account. Thus a better illustration is required for the clear understanding of this principle. In this article we illustrate Heisenberg's uncertainty principle with a new thought experiment that could be called as gamma ray telescope with the inclusion of properties of the lens and quantum nature of light.