The smallest of the common interchangeable-lens formats. Its featherweight sensor moves fast and far in its stabilizer, depth of field is immense, and long lenses stay small, which makes the format a favorite for birds and wildlife. Its limits: diffraction arrives early when stopping down, and serious low-light or night work wants a bigger sensor.
Softness that appears when the aperture is stopped down too far. Light passing through a large opening comes out in one coherent bunch, like water from a hose at low pressure; squeeze the opening down and the light begins to scatter at the edges, just as the hose starts to spray. Past a certain aperture that scattering blurs fine detail across the whole frame no matter how good the lens is. The smaller the sensor, the sooner it arrives.
Saved banks of camera settings that can be recalled with a dial position or button. Set one up for each situation you shoot often, and switching to it applies every stored setting at once. This avoids the classic failure: settings dialed in for one situation, then one of them forgotten when the situation changes.