1. An optical apparatus for determining the distance between the apparatus and a target for hand held firearms having fixedly attached thereto a housing supporting ocular and objective lenses at opposite ends thereof and at least one image erecting lens arranged therebetween for forming an erect image of said target at the rear plane of focus of said image erecting lens, said rear plane of focus of said image erecting lens being adjustably coincident with the forward plane of focus of said ocular lens with the optical axes of said lenses being common and lying essentially parallel to the bore of said firearm comprising: microcomputer means attached to said firearm including memory for receiving and storing permanent and temporary ballistic data, instructions pertinent to range-finding and other ballistic operations, means for computing range and compensation for aiming, and for generating a variety of signals relating to said computations performed relative to and by means of said data and instructions, data input means communicating with said microcomputer means for receiving temporary data and instructions pertinent to rangefinding computations from an operator and storing them in said memory for affecting computations performed by said microcomputer means in a manner compensatory of changes in said data, display means connected to said microcomputer means for selectively displaying indicia indicative of said signals generated by said microcomputer means superimposed upon the field of view of said apparatus viewable by the operator, rangefinding signal generating means controlled by said microcomputer means and associated with said display means comprising a plurality of closely spaced electronic indicator elements adjacent a single stationary visible reference indicator, said plurality of electronic indicator elements being controllably activatable by the operator so as to define a controllably variable space defined by said stationary reference indicator and an activated one of said plurality of electronic indicator elements, the images of said activated electronic indicator element and said single fixed reference indicator lying in a plane common with the forward adjustable plane of focus of said ocular lens of said apparatus so as to provide a focused image of the target superimposed upon focused images of said activated one of the plurality of electronic elements and said single fixed reference indicator all viewable simultaneously by the operator, said variable space being indicative of a relationship between a size of an image of the target and the distance or range of the target from the apparatus and being interpreted by said microcomputer means as a measure of the distance to the target, and said microcomputer means subsequently selectively activating one of said plurality of electronic indicator elements as a result of computations performed relative to said range interpretation and said stored data and instructions for generating a compensating aiming indicator viewable by the operator within the field of view of said apparatus along with the image of the target to facilitate improved accuracy in the aiming of said firearm.