To calculate the focal length of the camera lens, we can use the formula for the field of view: FOV = 2 * arctan(d / (2 * f)), where d is the size of the field and f is the focal length. We need to rearrange this formula to solve for the focal length f. Given the distance to the object and the dimensions of the field of view, indicating a 5 meter distance with a 2 meter vertical field and a 1 meter horizontal field, suggests that the effective focal length of the camera lens is closer to 5 meters.