About: http://webisa.webdatacommons.org/441364894

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	form of riflescope, the erector optics are also controllably movable along the optical axis within their tube in such a manner as to cause the focal length of the optical system to vary to provide an image of variable size.
http://www.w3.org/ns/prov#wasQuotedFrom	freepatentsonline.com