Choose your camera: you see the pixel size and the aperture from which diffraction starts to cost detail, with each f-number compared to the pixels.
Light bends at the edges of the aperture: a point becomes a small disc, the Airy disk, 2.44 × wavelength × f-number across (green light, 550 nm).
Once that disc is about twice as wide as a pixel, the finest detail starts to soften. It is gradual: one stop past the limit is still very usable, and sharpening hides some of it.
How much is sharp: near and far limits, hyperfocal distance and how blurred the background gets.
Field of viewSee what a focal length takes in on your sensor, drawn on a scene, with the angle of view.
Crop factor & equivalenceFull-frame equivalent focal length and aperture for every sensor size, both ways.
Handheld shutter speedThe slowest speed for sharp handheld photos with your focal length, sensor and stabilisation.