fixed focal length lens

Its distinguishing feature is its fixed focal length lens (non-zoom).

For all these reasons, the optical performance of zoom lenses tends to be lower than fixed focal length lenses.

Carl Zeiss' fixed focal length lenses are known for their high light sensitivity and precise manual handling, leaving the photographer in full control.

The design of a fixed focal length lens (also known as prime lenses) presents fewer challenges than the design of a zoom lens.

To a lesser degree, this effect is also seen in fixed focal length lenses that move internal lens elements, rather than the entire lens, to effect changes in magnification.

Lenses in the latter group of zoom lenses, sometimes referred to as "normal" zooms, have displaced the fixed focal length lens as the popular one-lens selection on many contemporary cameras.

The practice became popular in cinematographic usage before the advent of zoom lenses, where fixed focal length lenses were calibrated to T-stops: This allowed the turret-mounted lenses to be changed without affecting the overall scene brightness.

For example, telescopes that are marked "APO" are specialized, fixed focal length lenses that are optimised for infinity-like distances whereas in photography, even certain relatively low-priced general-purpose zoom lenses are given the APO designation.

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For example, a greater degree of barrel and pincushion distortion is tolerated in lenses that span the focal length range from wide angle to telephoto with a focal ratio of 10x or more than would be acceptable in a fixed focal length lens or a zoom lens with a lower ratio.