Edited sentence: A negative BFD indicates that the focal plane lies inside the lens.Consider a lenticular print that has lenses with 336.65 µm pitch, 190.5 µm radius of curvature, 457 µm thickness, and an index of refraction of 1.557.From Snell's Law,.In most cases, lenticular lenses are designed to have the rear focal plane coincide with the back plane of the lens.The angle of view of a lenticular print is the range of angles within which the observer can see the entire image.The angle outside the lens is given by refraction of the ray determined above.The back focal plane is located at a distance  from the back of the lens:.The condition for this coincidence is , or.The diagram at right shows in red the most extreme ray within the lenticular lens that will be refracted correctly by the lens.The focal length of the lens is calculated from the lensmaker's equation, which in this case simplifies to:.The full angle of observation  is given by.The full angle of observation  would be 64.6°.The lenticular lens in the example above has focal length 342 µm and back focal distance 48 µm, indicating that the focal plane of the lens falls 48 micrometers behind the image printed on the back of the lens.This equation imposes a relation between the lens thickness  and its radius of curvature.This is determined by the maximum angle at which a ray can leave the image through the correct lenticule.This ray leaves one edge of an image strip (at the lower right) and exits through the opposite edge of the corresponding lenticule.is the angle between the extreme ray and the normal at the point where it exits the lens,.is the distance from the back of the grating to the edge of the lenticule, and.is the lens's index of refraction.is the pitch, or width of each lenticular cell,.is the radius of curvature of the lenticule,.is the thickness of the lenticular lens, and.where  is the angle between the extreme ray and the normal outside the lens.where  is the focal length of the lens.where  is the index of refraction of air