Which lens type has a fixed iris opening size that cannot be altered?

The lens type that has a fixed iris opening size, which cannot be altered, is the Fixed Iris Lens. This lens is designed specifically with a constant aperture, meaning that the amount of light entering the lens remains constant regardless of the lighting conditions. This feature is beneficial in situations where consistent exposure is important, as it allows for consistent imaging quality without the risk of exposure variations that can occur with adjustable iris lenses.

A Fixed Iris Lens is commonly used in environments where lighting does not change much, ensuring that the depth of field and image quality remain steady. In contrast, other lens types, such as the Manual Iris Lens, offer adjustable apertures that can be changed by the operator, while Video-Iris Lenses can automatically adjust their iris based on lighting, allowing for dynamic control over exposure. P-Lenses do not specifically refer to a lens type with fixed iris characteristics and serve different functions in optical design. Overall, the Fixed Iris Lens stands out for its simplicity and reliability in delivering consistent imaging results.