A lens apparatus comprises a barrel 100 which houses an imaging optical system including magnification-varying lens units 26 and 27, a focus lens unit 25, and a beam separation element 29 which separates a part of a light beam from an object out of a light beam directed to an imaging surface, operating...http://www.google.com/patents/US7962028?utm_source=gb-gplus-sharePatent US7962028 - Lens apparatus and camera system
