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.
Camera aperture and shutter-speed controls are calculated so that an increase of one f/number compensates for a one-step decrease in shutter speed. For example, 1/250 at f/8 is equ*alent to 1/125 at f/11. The table below shows how aperture and shutterspeed are interrelated. All the combinations give the same exposure.