Fast Lens: What Is It, and Why Does It Matter?

Do you want to know what a fast lens actually is? And are you wondering whether you should be using fast lenses in your photography?

You’ve come to the right place.

In this article, I’m going to give you the lowdown on fast lenses, including:

• what they are
• what they offer
• and why you should (or shouldn’t!) use a fast lens in your own photography.

Let’s get started.

What is a fast lens in photography?

A fast lens refers to a lens with a wide maximum aperture. The larger the maximum aperture, the faster the lens.

Note: A lens’s aperture refers to a hole in the lens, which opens and closes depending on your camera settings. A wide aperture has certain special effects, and these are only offered by fast lenses.

Now, wide apertures correspond to low f-numbers, such as f/1.4, f/1.8, and f/2.8. Narrow aperture correspond to high f-numbers, such as f/5.6, f/8, and f/16. So if you see a lens with f/1.8 or f/2.8 in its name, you know that it’s a fast lens; if you see a lens with f/5.6 in its name, you know that it’s a slow lens.

Why does lens speed matter?

Fast lenses come with two main advantages:

1. Fast lenses allow you to use fast shutter speeds

A fast lens offers a wide aperture, and a wide aperture lets in more light – so you can capture well-exposed photos while using a faster shutter speed (compared to a slower lens, where you’ll need to reduce the shutter speed to get well-exposed photos, all else being equal).

This is invaluable when shooting handheld or moving subjects in low light. On a fast lens, you can widen the aperture to f/2.8, then dial in a motion-freezing shutter speed.

In fact, that’s where the term “fast lens” comes from; such lenses are so named because they allow for faster shutter speeds.

Note that a fast lens can also keep the ISO down, which prevents noise. If you can widen the aperture, you don’t need to boost the ISO for a good exposure, especially at night.

2. Fast lenses create shallow depth of field effects

The wider the lens aperture, the shallower the depth of field.

So if you set a fast lens down to its widest aperture, you generally get a strong shallow depth of field effect (which manifests as a highly blurred background).

This can be a good way to remove distractions from a scene, plus it just gives an interesting creative look.

Of course, if you prefer to work without shallow depth of field effects, you can; simply stop down the lens past f/4 or so, and the window of sharpness in your images will expand rapidly.

Should you use a fast lens?

Fast lenses are nice in certain situations, plus they offer plenty of shooting flexibility. But do you really need a fast lens for your camera bag? Or is it sometimes an unnecessary effect?

In truth, fast lenses can be burdensome, for a few key reasons.

Fast lenses are heavy and bulky

The faster the lens, the heavier and bulkier the lens, all else being equal.

As a consequence, faster lenses are difficult to work with, and so if you plan to go on a long hike or carry around equipment all day, working with a slower lens might be a good idea.

Fast lenses are more expensive

A fast lens can do everything a slow lens can do, and then some – so, as you might expect, fast lenses cost significantly more money than slow lenses.

Many professional lenses come in two versions, the fast version and the slow version, where the fast version offers an f/2.8 maximum aperture, and the slow version offers an f/4 maximum aperture.

Why pay for what you don’t need?

Fast lenses are sometimes unnecessary

Certain types of photography just don’t need fast lenses. If you always shoot with a tripod, for instance, a fast lens is pretty pointless, because you can always use a lengthy shutter speed without significant consequence.

There are also certain types of macro shooters who always use f/8 and beyond, so an f/2.8 aperture is mostly wasted.

Make sense?

Fast lenses: when should you use them?

To complete this discussion on the value of fast lenses versus slow lenses, I wanted to mention a few photographic genres where fast lenses are highly useful, as well as a few genres where fast lenses are unnecessary.

Here’s the list of genres that thrive off of fast lenses:

• Wildlife photography
• Portrait photography
• Sports photography
• Street photography
• Event photography
• Astrophotography

After all, fast lenses are perfect for situations with low-light handheld shooting and moving subjects.

Here’s a list of genres that don’t require fast lenses:

• Landscape photography
• Macro photography
• Architectural photography

In the above genres, shooting with an f/4 lens should work just fine!

Fast lens photography: final words

Well, there you have it:

Everything you need to know about fast lenses in photography.

Hopefully, you now feel like a fast lens expert, and you definitely know whether they’re right for you!

Do you plan on buying a fast lens? What do you like to shoot, and how will a fast lens help? Share your thoughts in the comments below!