CREDIT: ALLISON PEARCE
This photo demonstrates a shallow depth of field and how it brings out textures in the husk.

Any beginner photographer who has ever purchased different lenses for their camera has probably encountered the tantalizing question of why a 50mm f/1.4 lens is much pricier than a 50mm f/1.8. But why? What does it mean when a lens is fast? Why does the speed of a lens even matter? Why is a faster lens more desirable?

The speed of a lens refers to how large the hole in the lens can open. The opening is called the aperture, and it is measured in f-stops that usually range from f/1.4 (a large opening) to f/22 (a small opening) depending on the lens. Some may even be faster or slower. Aperture is measured by speed, because it is referring to how quickly a large amount of light can hit the sensor. Shooting at a low f/stop of around f/1.8 allows your shutter to operate quickly because the large opening allows a lot of light to hit the sensor very fast. This means that your camera can use a much quicker shutter speed to shoot your image. A fast shutter speed is advantageous, because it reduces the risk of a blurry image from handshake.

A “fast” lens, which is a lens that offers an aperture of f/2.8 or less, can also be advantageous over another lens with a smaller aperture because it allows for a shallow depth of field. A shallow depth of field is a powerful creative tool and is great for attracting attention solely onto the subject. This is especially great for portraits and close up nature shots. A deep depth of field, which you can achieve when you “stop down” or make the opening of your lens smaller, allows your entire image to be sharp and in focus. This is fantastic for nature shots and scenic imagery. Understanding which f/stop to use when allows you to have much more creative control for your images.

Now, you may be asking, what is a stop? Well, a stop is the size of the opening. Stopping down means making the opening in your lens smaller. The smaller the opening, the higher your f/number.

Modern cameras use a standardized f-stop scale, which is: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 and so forth.

Most cameras also allow the option to use increments in between stops. When you go down a stop – such as going from f/5.6 to f/8 – the lens is letting in only half of the light it was before. The same goes for when you open up your lens a stop – you’re allowing double the amount of light through your lens. This is why your shutter speed is faster when shooting with your lens wide open – a lot more light is being captured by the sensor a lot quicker and vice versa with a closed down lens.