amples of image formation in lenses. In the former case, an object at an infinite distance (as represented by a collimated beam of waves) is focused to an image at the focal point of the lens. In the latter, an object at the focal length distance from the lens is imaged at infinity. The plane perpendicular to the lens axis situated at a distance f from the lens is called the focal plane.If the distances from the object to the lens and from the lens to the image are  S1 and S2 respectively, for a lens of negligible thickness, in air, the distances are related by the thin lens formula1S1+1S2=1f{\displaystyle {\frac {1}{S_{1}}}+{\frac {1}{S_{2}}}={\frac {1}{f}}}   .This can also be put into the "Newtonian" form:x1x2=f2,{\displaystyle x_{1}x_{2}=f^{2},\!} [2]where x1=S1−f{\displaystyle x_{1}=S_{1}-f} and x2=S2−f{\displaystyle x_{2}=S_{2}-f}.What this means is that, if a