The present invention relates to a molding lens with indentation for measuring eccentricity and a method for measuring eccentricity thereof, especially to a lens with at least one indentation that is concentric with optical surface and is arranged on the area outside the optical surface. The indentation is observed by a measuring microscope. Thus by eccentricity test function of the measuring microscope, the eccentricity of the lens is obtained and the eccentric direction is defined so as to modify the lens mould.
Refer to FIG. 1, a manufacturing process of a molding lens A1 includes following steps: Firstly design front and rear optical surfaces A2 of the lens A1. For example, the optical surfaces A2 are aspheric surfaces having a concave surface and a convex surface. For example, an ultra-precision machine in combination with numerical control (NC) programming is used to define toolpath. That means to set sag value (tool depth) so as to conduct precision machine processing of moulds. As to a curvature lens, the Z-axis is an optical axis of the lens and center of surface is as zero point of X-Y plane. On different positions of the surface of lens, the height difference between a line parallel to the Z-axis and the X-Y plane is the sag value. Moreover, the sag value can also be calculated by equations such as Anamorphic surface, First Type Toric surface or Second Type Toric surface. Then by process of injection molding or die-cast molding, lens are mass produced. After finishing the mould, firstly samples are made to run an eccentricity test for mould modification. Furthermore, each of lens produced needs to go through the test procedure to make sure they are good products.
Refer to FIG. 2, a conventional eccentricity test of the optical surfaces A2 of the lens A1 is disclosed. A transmission eccentric scale indicator A3 in combination with a rotatable jig A4 is used so as to make a parallel light A5 from a light source on the bottom penetrates through the optical surface of the lens A1 being detected to form an image on a screen A6. The transmission eccentric scale indicator A3 is quite expensive so that the manufacturing cost is increased. The jig A4 clips the lens A1 being detected and carries it to rotate while radius of rotation of a focus A7 on the screen A6 is used as criteria for checking eccentricity. Thus the requirement on eccentricity of the jig A4 itself is quite high and the eccentricity of the jig A4 is no more than 2 μm (10−6 m). Thus the cost for the jig A4 is also quite high due to operation error of the jig that affects the eccentricity test results. Moreover, except the test results, the error of the jig A4 also have effects on quality control of the lens A1. Furthermore, conventional technology can only check eccentric scale of the lens A1 on the screen A6. The eccentricity of the front and the rear optical surfaces A2 can't be distinguished. Therefore, the eccentricity of the lens A1 on the screen A6 can't be used as modification index directly.
In other words, it is difficult to decide the eccentricity of the lens A1 derived from errors of which optical surface. Thus the optical surface on the mould can't be modified precisely or efficiently and this leads to trouble on mould modification.