[6-17] "Manual"

Before cameras got sophisticated, there were several kinks that needed to be worked out.

Somehow, a specific amount of "time" is needed for light exposure; a photographer can request 1 second, or 0.13 seconds, or 30 sec. For values under 1 second, an automatic system is preferable (better than placing your hand in front of the front element to reveal/block light).

This was the basis of a shutter.

The Nikon FM I used in college, purchased in the 70s, features a fully mechanical shutter. The snap and mirror movements are spring activated without a battery.

The stock lens was a 50mm without autofocus. One hand has to rotate the focus ring. The viewfinder has a split-screen prism (uncommon today) that allows the photographer to align straight objects for optimal focus. We now rely on the camera's computer to declare the edges are sharp.

An aperture can be "manually" adjusted, meaning the size of the lens opening can be dictated. Many decades ago, Nikon invented the "automatic diaphragm", keeping the lens at maximum brightness (largest aperture) and temporarily closing it only when a picture is taken. This occurs in a blink of an eye. As SLR requires the same lens for film and focusing, two needs must be prioritized.

In the DSLR, there is a manual option for ISO; a novice should build up from here.