Mastering Apertures 2

FAST OR SLOW LENSES
You may often hear the terms ‘fast’ or ‘slow’ to describe a lens or aperture. This has nothing to do with the speed of operation, but to the size of the maximum aperture possible (usually quoted as a suffix to the name of a lens). A lens with a maximum aperture of f/1.4, for example, is ‘faster’ than a similar lens with f/2.8. Because the aperture is larger, faster shutter speeds can be used, which is especially useful in low-light conditions.

Another practical benefit of a larger aperture is that the extra light that enters the lens leads to brighter viewing on the camera’s viewfinder – again, useful in low-light conditions.

Zoom lenses will often quote two maximum apertures, for example 18-70mm f/2.8-4. This means that the maximum aperture at the 18mm end is f/2.8, while the maximum aperture at 70mm is f/4. In reality, the actual hole is the same size but the added focal length (and the maths) changes the f-number. There are several lenses available now with a fixed maximum aperture that doesn’t change throughout the focal range, such as Sigma’s
70-200mm f/2.8 lens. These lenses are usually expensive though, and because of the large optics needed to perform the trick, quite heavy as well.

 Canon produces the excellent 85mm f/1.2 while Sigma’s 70-200mm f/2.8 lens has a continuous maximum aperture of f/2.8

APERTURE SIZES
Reducing the aperture size is often called ‘stopping-down’, while increasing the size is referred to as ‘opening-up’.