Full-frame sensor

Measuring about 36mm by 24mm, the sensor matches a frame of 35mm film, and everything people like about it follows from that size. At the same framing and aperture, focus falls away faster, so backgrounds melt more. Each pixel collects more light, so the image stays cleaner as the room gets darker. The costs are real. Bodies and lenses are heavier and dearer, and shallow focus is unforgiving when you are filming yourself with nobody watching the monitor. Sensor size is also the smallest lever available. A cheap camera in good light beats a full-frame one in bad light, every single time.