2. Viewfinder
The viewfinder optics consist of an eye lens, a concave mirror and a wafer lens (Figure 2-4). As in all simple optical system, a certain amount of distortion is inherent in this design. A small wafer lens is introduced into the viewfinder optical path to limit to angle of acceptance and, thus, reduce distortion. The size of the lens opening is large enough to provide acceptable viewing brilliance and, at the same time, small enough to be easily closed when the camera is in the exposure mode. (On earlier models a rectangular mask called a stigmatic pupil takes the place of the wafer lens.
Figure 2-4 Wafer lens assembly
Ignoring the shutter functions momentarily, when the operators presses the exposure button, the Fresnel carrier swings away from the film plane and comes to rest in front of the viewing mirror. During the moment of the Fresnel carrier (and until it returns to its initial viewing position), a flexible light stop closes a path between the viewfinder and the inner camera to prevent light trough the eye lens from reaching the film. The movement of the spring-driven Fresnel carrier is accomplished by the motor-driven gear train. The details of the automated action are described in the discussion of the electro / mechanical assemblies.
3. Mirrors
Two first surface mirrors are used in the SX-70 optical system. When a picture is being taken, the Fresnel carrier is raised. This places the 4-edges taking mirror into the optical path and light is reflected onto the film plane. (The taking mirror is mounted on the Fresnel carrier on the side opposite the Fresnel screen.) The second
mirror, the 6-edges viewing mirror is used in the optical path twice. First, the light rays entering the camera from the taking lens are reflected onto the Fresnel screen by the viewing mirror. Secondly, the operator views the image on the screen with light reflecting off the viewing mirror (Figure 2-1). (The viewing mirror is located on the underside of the mirror cover assembly.)
4. Flare baffle
The flare baffle (Figure 2-2) is a spring-loaded plate which springs up when the Fresnel screen moves into the picture-taking mode. In this state, light is prevented from passing through the lens directly onto the film without first being reflected off the taking mirror. This prevents «hotspots» from appearing on the finished picture. When the Fresnel carrier is in the lowered position, the flare baffle is held down, out of the optical path.
E. CAMERA ELCTRONICS 1. General
The SX-70 is unique, both in its principles of operation and its functional design. It can be considered as aan electronically controlled mechanical device. An electronic control module (substrate or ECM) contains all of the electronic components with the exception of the motor control (MCC) integrated circuit and the flash fire assembly (FFA). Because the ECM is located inside the shutteur housing, it becomes identified as part of the shutter (Figure 2-5). It should be noted that all of the camera automation is controlled by the integrated circuits in the ECM.
Figure 2-5 ECM - Electronic Control Module
