The wonderful thing about framing is that it has served painting in times before photography. External viewfinders have been around since before cameras were invented, and they have been around longer than cameras! The viewfinder adds a boundary to your field of view, which gives you the right to choose your field of view.
Leica’s external viewfinder is a reverse Galilean structure made up of four groups of five lenses. The wireframe is really bright and the light comes from the internal reflective concentrator lenses. Just a heads-up: when you use it, the distance between your eyes and the viewfinder is 8 millimeters, and you can’t cover your eyes completely.
I am partial to carrying this early Leica SBLOO 35 mm viewfinder. In the early days of Leica, each focal length viewfinder was given a distinctive name. For example, the 50 mm was designated as SBOOI, the 35 mm as SBLOO, the 28 mm as SLOOZ, the 21 mm as SBKOO, the 90 mm as SGVOO, and the 135 mm as SHOOC.
