Perspective errors, or parallax, are part of everyday human experience.
In fact, they let the brain interpret the 3D world. For example, closer objects to appear relatively larger than those away. This phenomenon is also present in imaging systems in which the size of an object changes with its distance from the lens. Telecentric lenses, such as those from Edmund Optics, Barrington, N.J. (edmundoptics.com), optically correct for this, an important capability for machine-vision systems. The lenses keep objects the same size regardless of their location with respect to the lens, as long as they are positioned within the range of the lens. Maximum field of view is a function of lens diameter, so telecentric lenses are quite wide.
Edmund lenses have 0.2° or less of telecentricity when used within the lenses working range. They also feature a front filter thread for adding color filters, polarizers, and other machine-vision components. Aperture and focusing adjustment can be fixed by setscrews.