In the first part of the experiment, table part A, we determined the focal length of the lens using an object at infinity. We used thesunlight from the window as an object at infinity. We adjusted the lens until a sharp image of the window is formed. We determined the image distance. The focal length is equal to the distance of the image projected on the screen from the lens. The first methodtells that when the object is at infinity(s=infinity sign) the focal length f is automatically equal to the image distance. This is because of the thin lens equation, 1f=1s+1s'. Knowing that s=infinity sign, 1/(infinity sign) is zero. Therefore, (1/f)=(1/s’). Getting their inverse will result to f = s.In the second part of the experiment, table part B, we determinedthe focal length of the lens using an object at a finite distance (light source). We moved the convex lens, starting from the light source, until a sharp image is formed on the screen. After getting all the data on that position, we moved again the convex lens away from the light source until another sharp image is formed.