Abstract: An optical attachment having five or six elements and configured to be operably arranged on the image side of an objective lens to reduce the focal length and focal ratio of the objective lens is disclosed. The optical attachment is particularly suitable for adapting objective lenses designed with a relatively large working distance for a large format size to cameras having a smaller format size and relatively small permissible working distance. The optical attachments disclosed herein have high image quality at large aperture over a large field of view, and can be well-corrected for all major aberrations.

Abstract: An optical attachment configured to be operably attached to the image side of an objective lens to reduce the focal length and focal ratio of the objective lens. The focal-reducing attachment includes four lens elements and has a magnification of between 0.5 and 1. The focal-reducing lens can work with objective lenses having relatively large working distances for a large format size as well as with cameras having a smaller format size and relatively small permissible working distance.

Abstract: A corrective optical system for an imaging optical system is disclosed, wherein the imaging optical system has an objective having a working space, and whose imaging performance is not corrected for one or more plane parallel plates located in the working space. The corrector optical system resides in the working space between the one or more plane parallel plates and objective and serves to reduce the aberrations introduced by the one or more plane parallel plates. The corrector optical system enables objectives originally designed for film to be used with digital cameras.

Abstract: Large aperture optical systems that are extremely well corrected over a large flat field and over a large spectral range are disclosed. Breathing and aberration variation during focusing are optionally controlled by moving at least two groups of lens elements independently. Aberration correction in general is aided by allowing the working distance to become short relative to the format diagonal. Field curvature is largely corrected by a steeply curved concave surface relatively close to the image plane. This allows the main collective elements to be made of low-index anomalous dispersion materials in order to correct secondary spectrum. In wide-angle example embodiments, distortion may be controlled with an aspheric surface near the front of the lens.