The Argus is a small plate camera, disguised as a monocular, and designed to take photographs covertly, at right angles to the direction the monocular appears to be pointed. It was made by Nettel Camerawerk in Sontheim, southern Germany, from about 1909. The model was continued by Contessa-Nettel, who later renamed it the Ergo, and under this name by Zeiss Ikon.
The camera takes 4.5x6 cm plates in single dark slides. The lens is either one of Nettel's own Anastigmats or Rapid Aplanats, or an f/4.5 Zeiss Tessar. In early cameras, there are only two aperture settings; for example f/4.5 and f/9, selected by a lever on the body. The shutter of the early camera is a simple 'I' and 'B' one.
Later cameras by Contessa-Nettel and Zeiss Ikon have a full range of apertures, selected with the rim of the false 'front lens' of the monocular, more shutter speeds (up to 1/100 second), and a focus control.
- Nettel Argus with f/4.5 Tessar; two aperture settings f/4.5 and f/9; and both right-angle finder and a Newton finder; sold at the eighteenth Westlicht Photographica Auction, in December 2010.
- Contessa-Nettel Argus] with f/4.5 Tessar, full aperture range to f/36, shutter speed dial, chrome focusing knob and both right-angle finder and ground-glass focusing hood, sold at the sixteenth Westlicht auction, in December 2009.
- Zeiss Ikon Ergo with focusing 5.5 cm f/4.5 Tessar, about 1928, sold at the tenth Westlicht auction, in November 2006.
- Nettel Argus with plateholders, tripod adapter and leather case, sold at the sixteenth Westlicht auction in December 2009, showing screw-holes where a folding viewfinder may have been removed.