Toronto. Most of the early cameras were big boxy things with relatively small diameter lenses. Early on you changed lenses to change angles of view (wide angle, telephoto) always mindful of the diameter of the circle of confusion – or how much of the plate could be covered without vignetting. Stopping down a lens would improve its coverage
To focus on both near objects and infinity, the awkward old cameras had to be adjusted. The two most common approaches were the box-in-a-box and the bellows. As cameras shrunk in size, the so called normal lens became shorter. For a brief time both bellows and threaded metal focussing mounts were used. As the minicam revolution in the 1930s took off, threaded metal focussing mounts took over the market. Extension rings, bellows, and auxiliary lenses were used to allow close-ups closer than about one metre – the common near focus distance of a minicam such as the Leica.
In the above photo, you see the distance scale for a Poco camera allowing the lens to be focussed at distances shorter than infinity.
Modern day smart phone cameras are automatically focussed internally leaving most users with little if any interest in how the technically sophisticated little wonders accomplish such focussing from infinity to a few inches. They are marvels with about a 3mm focal length lens (equal to a 35mm lens or even shorter today) and auto focussed using a square box outline and finger tap on the gorilla glass screen.