What is a “fast lens”?
“Fast lens”, “fast glass”. What does that mean?
People often refer camera lenses as “glass” because lenses are made of glass.
A fast lens simply is a nickname for a lens with a large maximum aperture. Lenses with a maximum aperture of f/1.2, f/1.4, f/1.8, f/2.0, or f/2.8 are considered fast.
What does aperture have to do with being “fast”?
Large aperture means the lens opens up wide to let in more light to the camera sensor which allows you to use a faster shutter speed.
Let’s say I’m using a not so fast lens with a maximum aperture of f4.0. I’m photographing in a lighting condition where my camera setting needs to be at ISO 2000, shutter speed 1/40 and my aperture at its widest f/4.0. At a slow shutter speed 1/40, I’m concerned about getting a lot of shaky photos due to movement or motion blur.
If I were to use a “fast lens” at aperture f/2.0 under the same lighting conditions, I’d be able to raise the shutter speed to 1/160 and get the same exposure without having to worry too much about motion blur.
Here are some fast lenses that I’d recommend for Canon or Nikon DSLR cameras.