Abstract\noindent It was required to measure the focal lenghts of different lenses that are in the optics laboratory, each one of this lenses have a thoerical focal lenght provided by the fabricant; to measure and check these lenghts an experimental arrangement was placed with a rail mounted to place the lenses, a laser and a screen. The focal lenghts were measured and checked succesfully, leading us to the image formation of each lens using the same arrangement, but instead of the laser, an halogen ligh source was used. The different images and magnifications were obtained due to different distances of the lamp placement.