Aperture is the size of the lens opening that lets light through. Smaller f-numbers (f/1.8) mean larger openings, more light, and shallower depth of field.
Aperture progression: f/1.4 → f/1.8 → f/2.0 → f/2.8 → f/4.0 → f/5.6. Each stop halves the light.
Wider aperture (smaller f-number) benefits: low-light photography, subject isolation (background blur/bokeh), faster shutter speeds.
Smartphone main cameras typically range f/1.5–f/1.8. Telephotos often f/2.8–f/3.5. Variable apertures (Samsung Galaxy S Ultra series with f/1.4–f/2.4) trade light gathering for sharper landscapes.
DSLR/mirrorless lenses with f/1.4 aperture can isolate subjects dramatically — a look smartphones imitate via computational portrait mode.