Tech Check Fast lens
There can be confusion about what this term means, so let’s clear it up
What is a fast lens?
It’s a common misconception among newcomers to photography that a fast lens refers to an optic’s ability to focus quickly, but this isn’t the case. If a lens is referred to as fast, it means that it has a wide maximum aperture, typically f/2.8, but also potentially f/1.8 or f/1.4.
So where does the term ‘fast’ come from?
It simply refers to the ability of the lens to achieve faster shutter speeds in low light by opening the aperture up to its widest setting. This means when the hole (aperture) in the lens through which light passes on its way to the sensor is physically at its largest.
Why aren’t all lenses fast?
As a general rule, the extra material that’s required to create a fast lens pushes the price up, and it’s not uncommon for most manufacturers to have an expensive fast lens than a more reasonably priced one, but with a smaller maximum aperture. Fast lenses are also often referred to as professional lenses, and some are labelled ‘Pro’, but of course you don’t have to be a professional photographer to enjoy using them.
Do I really need to use a fast lens?
Not necessarily – it all depends on the type of photography you enjoy and what you want to achieve. The improvement in noise control at higher ISO settings means you get faster shutter speeds in low light without necessarily always needing to open your aperture right up. That said, the limited depth of field (through the image sharpness) you can get with a fast lens is a way to shoot really pleasing and creative images where backgrounds are diffused.
Which areas of photography are best for fast lenses?
For creative control and fast shutter speeds in difficult lighting, fast lenses are particularly favoured for portraiture, wildlife and sport.