What is key of the focusing iris?

The key of the focusing iris is its ability to adjust the aperture size of a camera lens. As the aperture size is adjusted, the amount of light entering the lens changes which affects the depth of field and sharpness of the image. The focusing iris is typically controlled by a dial on the camera body and is used by photographers to achieve the desired effect in their images. A larger aperture (smaller f-number) creates a shallower depth of field, while a smaller aperture (larger f-number) creates a deeper depth of field. The focusing iris is an important tool for photographers as it allows for creative control of the final image.