Leave it to the world of photography to confuse size and speed. In lens-speak, the term “fast glass” refers to lenses with large apertures. In this article we take a look at the lenses with the largest-opening apertures. The aperture is the opening of a lens. The aperture’s size is expressed as a number that shows the ratio of the opening to the lens’s focal length. This number is referred to as an f/number, f/stop, focal ratio, f/ratio, or relative aperture.
What Does a Fast Lens Give You?
These large-aperture lenses are referred to as “fast” because they allow cameras to take photos at relatively fast shutter speeds for a given amount of ambient light. A fast lens might make it possible to take photos handheld in low light. Faster shutter speeds offer greater options for freezing action and can minimize camera shake, both of which can cause blur in your images, no matter how bright the scene. A large aperture also means that you can photograph with very shallow depth of field.
Why Would You Want a Fast Lens?
If you ever do off-tripod low-light photography, maybe at a concert or night club, you will want a lens that can open wide to maximize light gathering. Wedding photographers often find themselves in less-than-ideal lighting scenarios at the church or reception and need larger apertures, too. Street photographers working at dusk or dawn may benefit from more light striking the sensor or film. Finally, sports photographers working to freeze action and isolate subjects will appreciate large apertures.
Glass is heavy, which leads to an increase in weight when a lens is built with larger glass elements. More significantly, optical elements are also the most expensive part of a lens, so fast glass usually arrives with a premium price tag.
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