EF LENS TECHNOLOGY EF lenses are a product of Canon's dedication to innovative lens design. They complement the advanced technology incorporated in Canon EOS cameras, making it easier to take outstanding photographs. The fully electronic EF lens mount is unique among 35 mm cameras -- it has a series of electronic contacts, giving silent operation and unmatched reliability. Development of High-Performance EF lenses The development of the EF lens underwent a very thorough process. The concept is carefully studied from both the standpoint of the user -- i.e., focal length, zoom range, aperture ratio, closest shooting distance, required imaging performance, size, weight, cost, etc. -- and the standpoint of the developer and manufacturer. Since EF lenses combine optical, mechanical and electronic technologies, designers in charge of various areas such as lens barrel design, lens drive design, electronic control circuit design and industrial design work closely together from the initial design stage through the entire development process to produce an optimum lens. Actual EF lens design and development processes Optical lens design Figure 1 shows the lens optical design process used by Canon. Once basic specifications such as focal length and maximum aperture are set, the "lens type" is determined. This is where the structure of the lens is decided. The selected structure is a general conjecture of what structure the lens will likely have, but since it has a large influence on the subsequent process flow, a large-scale computer is used to search every possible lens type with an originally-developed evaluation algorithm used to select the optimum solution. Next, the process proceeds to the initial design stage where the optimum solution is analyzed based on Canon's own near-axis theory and aberration algorithms, and the initial shape of each lens element is determined. Since this stage is the most important part of the design process flow, Canon utilized analytic solutions based on theory, a rich databank of accumulated data and years of accumulated design experience to establish a system which can determine the ideal final configuration in a short amount of time. Once the initial lens configuration is determined, a super-high-speed large-scale computer is used to repeatedly perform the following design cycle : Ray Tracing ---> Evaluation ---> Automated Design --->Type/Shape Change ---> Ray Tracing In this process, as shown in Figure 2, the computer methodically varies each parameter (lens construction factor) such as the curvature of each lens surface, the surface interval (thickness) of each lens, each lens interval, and the material characteristics of each lens to gradually progress toward the optimum design configuration where every type of aberration is reduced to a minimum. Although this process requires the most complicated and largest volume of calculations in the entire design process, it can be carried out interactively and efficiently with today's advanced computers. The automated design software developed by Canon makes it possible for the optimum solution obtained in a short time by simply inputting the target values. Our designers interact with the computer to repeatedly make accurate judgments for near-ideal design values. The effect of using aspherical lenses or special material such as fluorite or UD (Ultra-low Dispersion) glass can also be thoroughly considered during the process, enabling designers to determine the necessity of their usage.