The OM-1 is an all-mechanical SLR. It has a large viewfinder with interchangeable screens but a fixed prism. It also has a through-the-lens exposure meter controlling a needle visible in the viewfinder. It has a compact body, essentially retained on later models. The shutter speed dial is located around the lens mount, which allows photographers to keep the camera at the eye between shots more easily than SLRs with the dial located on the top plate.