Constantaperture

Constantaperture is a term often encountered in photography and optics, referring to a lens or optical system where the aperture size, and thus the focal ratio, remains fixed regardless of the focal length. This is in contrast to zoom lenses that typically have a variable aperture, meaning the maximum aperture changes as the focal length is adjusted.

Lenses with a constant aperture are highly valued for their consistent performance across their entire zoom range. This means that the amount of light entering the lens is the same whether the lens is at its widest or longest focal length. This consistency is particularly beneficial in low-light situations, as it allows photographers to maintain faster shutter speeds or lower ISO settings without needing to adjust the exposure. It also simplifies exposure calculations, especially for videographers who need stable exposure during camera movements or zoom adjustments.

Achieving a constant aperture in a zoom lens typically requires a more complex optical design and often results in larger, heavier, and more expensive lenses compared to their variable aperture counterparts. Despite these drawbacks, the advantages in terms of light-gathering capability and ease of use make constant aperture lenses a preferred choice for many professional photographers and videographers. Examples include common zoom ranges like f/2.8 or f/4 throughout the entire zoom.