>>3888628>>fast>The fuck does that mean.>>3888630>Perhaps You should learn the basics before you worry about buying anything>>>3888632>Or perhaps you should pick a dictionary and read the meaning of the words you use.Everyone was new once, and so I will explain that term instead of just mocking you for not knowing it.
"Fast" when referring to a lens refers to having a wide aperture.
The aperture is the (basically) the size of the lens opening that lets in light, so a wider aperture lets in more light.
(For Math reasons, a smaller f/number means a wider aperture, and they increment by factors of the square root of two, or about 1.4. So, f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, etc)
Since a lens with a large aperture lets in more light, you can use a shorter shutter speed to get the same exposure. E.g,. if you need a shutter speed of 1/50th of a second at f/4, going one stop larger to f/2.8 means you only need a shutter speed of 1/100th of a second.
Since each leg of the exposure triangle directly affects the others, and since so much of photography in practice is desperately trying to find enough light to get a shutter speed that's not blurry, it's extremely common to refer to a lens with a large maximum aperture (f/2 or larger for prime lenses, f/2.8 or larger for zoom lenses) as "fast" because it allows for a fast shutter speed.
