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John Bowen
10-Dec-2014, 06:44
Optical attachment for reducing the focal length of an objective lens
Patent No. 8,903,232
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.
Inventors: J. Brian Caldwell (Petersburg, Va.)
Assignee: Caldwell Photographic Inc. (Petersburg, Va.)
Dec. 2, 2014

Dan Fromm
10-Dec-2014, 07:32
It is on the market. See http://www.metabones.com/products/?c=speed-booster

John Bowen
10-Dec-2014, 08:24
Thanks, Dan!