What phenomenon can inadvertently be added to a lens if it is tilted during the surfacing process?

When a lens is tilted during the surfacing process, the phenomenon that can be inadvertently added is known as prism. This occurs because the angle at which the lens is produced can affect how light is refracted through it. A properly aligned lens allows light to travel through it uniformly, creating clear vision. However, if there is a tilt, the optical center may no longer be aligned with the intended axis of the lens. As light passes through the surface of the lens, this misalignment causes a deviation in the direction of light rays, resulting in a prism effect. This effect can lead to unwanted visual distortions, making it crucial to maintain proper alignment during the surfacing process to avoid the introduction of prism that could disrupt the wearer’s vision.

Other phenomena, such as vignette, blur, and distortion, are related to different visual issues but are not directly caused by tilting the lens during surfacing. Vignette typically refers to a gradual darkening of the corners of an image, blur pertains to a lack of sharpness, and distortion involves irregularities in how images are represented, which can occur due to lens design rather than misalignment during manufacturing.