Cellphones
Although cellphones can’t make calls, utilize GPS, or do anything requiring a network connection while underground, they are all equipped with cameras, and virtually everyone owns one. The sensors on phones are quite small, so they have some inherent disadvantages in low-light conditions, but there have been significant advancements in “computational photography” that is allowing the small sensors on cellphones to increase sensitivity while filtering out noise. Most modern phones have cameras that can record 4K resolution, slow-motion, and are equipped with both mechanical and electronic image stabilization. They are increasingly also being made more rugged and waterproof, and durable cases are commonly available. Many phones are also now being released with wide angle lenses that are better suited to the field-of-view that is useful in caves. The video quality from a cellphone is still going to fall behind that of a larger sensor camera, and good quality external lighting is also still a necessity.