What are the key differences between the Nikon D810 and D3300 cameras?

The key differences between the Nikon D810 and D3300 cameras are in their sensor size, resolution, autofocus system, and overall features. The D810 has a full-frame sensor, higher resolution (36.3 megapixels), more advanced autofocus system, and additional features like a larger ISO range and better build quality compared to the D3300, which has a smaller APS-C sensor, lower resolution (24.2 megapixels), basic autofocus system, and fewer advanced features.