Film magazine in Arri SRI is connected from the back, and the pressure plate resides on the magazine. The film (left) runs between two guides made of Inkanel. In arri SR3 there are (4) Sapphire rollers at each end of the film gate.
Above, 100ft 16 mm film spools, and other accessories. Arri SR offered built-in light meter that drove a servo motor for automatic iris control on lenses. This was a challenging engineering task, but was so useful because as the frame speed was changed, the servo motor automatically changed the iris for exposure compensation. Professionals hardly ever utilized this feature in SR cameras.
The viewfinder in Arriflex SR I, SRII, and SR3 uses a rotating Schmidt Pechan prism to compensate for image rotation while the eyepiece angle was adjusted for viewing comfort, keeping the image always horizontal. There is also a tilting mirror that moves the image at half angle while the eyepiece is tilted horizontally, always keeping the image centered inside the eyepiece.