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.
1 If the focal length is 50mm, then, the minimum shutter speed would 1/50s (1/60s). ( 2 not the corrected focal length for the sensor size). 3  For the focal length of 250mm, then, the minimum shutter speed would be 1/250s. 4  Adapting this guide to modern DSLRs with sensors that are smaller than full frame sensors.