The optical design of a 3X zoom lens suitable for incorporation into a modern smartphone is described in detail. Particular emphasis is applied to techniques for achieving the required small size, extremely high image quality and the need to maintain at least an f/2.8 speed throughout the zoom range so as to minimize image quality loss due to diffraction. Because modern camera software allows for the correction of certain types of off-axis chromatic and distortion aberrations, optical designs offering both full and partial correction of these aberrations are presented. With such correction being obtained within the camera, optical designs containing fewer than ten lens elements are attainable, making the optical complexity comparable to that of current two-lens non zoom solutions. The presentation will include complete optical designs together with full prescriptions and illustrations of image quality.
Zoom projection lenses have been designed that have an entrance pupil that remains stationary during zooming and an operative aperture stop distinct from the system's physical stop that moves through the lens surfaces as zooming takes place. The fixed entrance pupil allows for efficient coupling to the light source throughout the magnification change. By allowing the stop to move through the lens, the lens element sizes and aberration contributions can be minimized. The concept of the operative stop can be employed for both positive and negative first-group configurations. For wide angle projection of 64 degrees total angle, a lens system with a negative front group followed by a positive zooming group has been designed with a relative aperture of f/4.5. Applications involving large LCD panels as light valves require the use of plastic optical materials with aspherical surfaces to minimize manufacturing costs. Concentrated high wattage light sources introduce temperature variations that impose additional constraints on the optical design. By combining plastic and glass elements the image position and aberration correction are stabilized throughout a plus or minus 25 degree Celsius temperature change.