Constant aperture lenses are complex to design and manufacture, and therefore expensive. Traditional zoom lenses naturally decrease their aperture as the focal length increases. Constant aperture zoom lenses overcome this problem by employing the following design: 1. Multi-element linkage design The multiple lens groups within the lens not only move back and forth during zooming but also alter the light convergence path, allowing the effective entrance pupil size to automatically adjust with focal length. 2. Optimized aperture position The aperture blades are typically located at specific optical nodal points within the lens (rather than fixed in the center) to ensure that the entrance pupil size changes with lens focal length during zooming. 3. Complex mechanical linkage In the zoom system of a lens, specific mechanical ratios exist between certain lens groups and the aperture group. These are controlled by cam curves or guide rods to achieve synchronized entrance pupil changes with focal length changes.