Ideally, a hydrogen fuel-cell vehicle has no environmental impact. Energy is produced by combining hydrogen with oxygen pulled from the atmosphere, and the tailpipe emission is water. The hydrogen fuel could come from a number of sources (Iceland recently started pulling it out of the ground).
4) Fast, Slow and Long Shutter Speeds. Fast shutter speed is typically whatever it takes to freeze action. For me, it is typically above 1/500th of a second for general photography and above 1/1000th of a second for bird photography. NIKON D700 @ 420mm, ISO 450, 1/2000, f/5.6.
The two components it uses to do this, the aperture and shutter speed, are also present on conventional cameras. 1  Aperture: The size of the opening in the camera. The aperture is automatic in most digital cameras, but some allow manual adjustment to give professionals and hobbyists more control over the final image. Shutter speed: The amount of time that light can pass through the aperture.