A lens changeover mechanism for use in a photographic camera, including a master lens and a conversion lens. The mechanism further includes a changeover ring, a lens barrel which is axially movably fitted into the changeover ring, a focusing member, a focus guide which is slidably supported, for focusing...http://www.google.com.tw/patents/US4482228?utm_source=gb-gplus-share專利 US4482228 - Lens changeover mechanism for use in photographic camera
