lovelifey: [Photography] Lens Sweet Spot: How to Find Your Lens’s Sharpest Aperture

The post Lens Sweet Spot: How to Find Your Lens’s Sharpest Aperture appeared first on Digital Photography School. It was authored by Dena Haines.

Are you tired of blurry images? Are you looking to capture consistently sharp photos, no matter your lens type?

There’s a simple solution: You need to find your lens’s sharpest aperture, also known as your lens’s sweet spot.

In this article, I share several methods of determining this ideal aperture. I also discuss additional reasons why your photos might be blurry (so you can deal with any and all issues right from the get-go).

By the time you’re done reading, you’ll know how to capture tack-sharp photos with every one of your lenses.

Let’s dive right in!

What is a lens sweet spot?

A lens sweet spot refers to the aperture at which a lens is sharpest.

You see, as you move throughout a lens’s aperture range, image sharpness changes. A lens is rarely tack-sharp throughout its entire range; instead, there’s generally an ideal aperture at which the lens produces outstanding results.

(Why? The answer is a bit technical, but it has to do with various optical aberrations and issues, such as spherical aberration and diffraction.)

Take a look at the two clock images below. Do you see how the image on the left is slightly softer than the image on the right? That’s because my lens’s sweet spot is f/9, not f/3.5!

Bottom line:

Every lens has an optimal aperture, a sweet spot at which images display top-notch sharpness. Of course, some lenses do remain relatively sharp as you adjust the aperture, but even the best lenses are slightly sharper around their sweet spot. The opposite is true, as well: while a low-priced kit lens probably won’t offer mindblowing sharpess at any aperture, it will improve when set to its optimal aperture.

Should you always use your lens’s sweet spot?

Using your lens’s sharpest aperture can significantly improve your images, but it’s important to know when a sweet spot is useful – and when it’s best ignored.

If your goal is to capture maximum detail – you’re doing landscape or product photography, for example – then shooting at your lens’s sweet spot can make a big difference. This is especially true if you plan to crop your photos (as sharper images will stand up better to significant cropping).

a snow scene shot at different apertures

It’s also important to maximize sharpness if you plan to print your photos large (because an enlarged image will often reveal your lens’s optical flaws).

However, extreme sharpness is far less important if you only ever plan to share your photos on social media or even on a portfolio website. Standard web file sizes don’t offer enough detail to really evaluate lens sharpness. Yes, it’s possible to see image blur in a web file, but such issues are generally due to photography technique, not lens optics.

Also, certain types of photography actually encourage blur; here, maximizing image sharpness can actually be detrimental. I’m talking about genres such as portrait photography, where a bit of softness can give your subject a beautiful glow and de-emphasize wrinkles and blemishes. Soft-focus macro photography, too, can benefit from a bit of blur, which can help create interesting artistic effects.

Finally, lens sweet spots tend to sit around f/8, but in certain situations, you’ll want to widen your aperture to f/4, f/2.8, or even f/1.4. Perhaps you need a wide aperture to shoot in low light, or you’re after a beautiful shallow depth of field effect. When you encounter such scenarios, you’ll need to think hard about whether lens sharpness is worth the tradeoff – or whether it’s worth sacrificing lens sharpness to achieve some other effect. Photography is often about compromise and sacrifice, and sharpness, while nice, isn’t the only thing that matters.

So before spending time obsessing over sharpness, ask yourself: How important is sharpness to me? Do I need to crop? Do I need to print large? Do I need maximum detail? Do I want a shallow depth of field? And depending on your answers, determine the right way to proceed.

How to find your lens’s sharpest aperture: two methods

In this section, I offer two ways you can identify your lens’s sweet spot. The first is a simple calculation that relies on a rule of thumb, while the second is more involved (and more accurate).

Go two stops beyond the maximum aperture

Every lens features a maximum aperture, the widest f-stop value it’s capable of achieving.

And while the lens’s maximum aperture tends to be relatively blurry, you can often reach the sweet spot by narrowing the maximum aperture by two stops.

So start by identifying your lens’s maximum aperture. (This is generally listed in the name of the lens; it’s also generally printed on the side and/or end of the lens.)

Note that all prime lenses feature a single maximum aperture, such as f/2.8 or f/4. But some zoom lenses, especially kit lenses and other zooms designed for beginners, will feature a variable maximum aperture. In such cases, the maximum aperture will change depending on the lens focal length. The listed maximum aperture range corresponds to the maximum aperture at the lens’s widest focal length and the maximum aperture at the lens’s narrowest focal length.

For instance, my Canon 18-55mm zoom lens has a variable maximum aperture of f/3.5 to f/5.6. At 18mm, the maximum aperture is f/3.5; at 55mm, the maximum aperture is f/5.6. You can see this range indicated on the front of the lens:

Once you’ve determined your lens’s maximum aperture, simply count down by two stops. You can use this chart, which counts by 1/3rd stops:

f/1.2
f/1.4
f/1.8
f/2
f/2.2
f/2.4
f/2.8
f/3.2
f/3.5
f/4
f/4.5
f/5
f/5.6
f/6.3
f/7.1
f/8
f/9
f/10
f/11
f/13
f/14
f/16

So count six steps from your lens’s maximum aperture to find its sweet spot. On my 18-55mm lens, the widest aperture is f/3.5. By counting down six steps (two full stops), I get a sweet spot of f/7.1.

This is a decent approximation of a lens sweet spot. And you can bank on your calculated sweet spot, plus a stop or so around the sweet spot, achieving very nice sharpness.

Aperture setting on canon LCD screen sharpest aperture

But if you really want to maximize detail, you can get a more accurate result with a test:

Do a careful sharpness test

Lens sharpness tests are easy to conduct, especially if you’re simply looking to determine the sharpest aperture.

First, mount your camera and lens setup on a sturdy tripod.

Next, place a simple subject about five to eight feet in front of your lens. If possible, select a subject that includes words (for instance, a person holding a newspaper). If you want to get really precise, then purchase a lens test chart, tack it to a wall, and shoot that.

For my test, I had my daughter hold a cup with writing on the side:

Find your lens sweet spot for sharper images tea cup at different apertures

Set your camera to Aperture Priority mode, dial in your camera’s base ISO, then set your lens to its maximum aperture. Before shooting, be sure your camera is using its two-second timer (you don’t want any camera shake ruining the test results!).

Aperture priority on Canon mode dial — Make sure to set your camera to Aperture Priority mode before shooting!

Finally, begin taking photos. Capture a few shots at each aperture (three photos is generally good). Then narrow the aperture slightly and continue. Work through the lens’s entire aperture range.

When you’re done, pull up the images on your computer and zoom in to 100%. Compare the images. Which look the sharpest? If you’re struggling to tell, you can always zoom in further. Pay particular attention to any text in the images, as that’s where softness will often be most visible.

By the way, be sure to check both the center and the edges of your files. Lenses tend to lose sharpness as you move out from the center of the frame, and it’s important to understand how aperture affects edge sharpness, too.

Eventually, you’ll determine the sharpest aperture. Be sure to commit this number to memory (and write it down, just in case!). The next time you need to produce tack-sharp images, it can be your go-to aperture setting.

Why are my images still blurry?

If you’ve identified your lens’s sharpest aperture but you’re still getting blurry images, then you’re likely dealing with one of a few possible issues.

First, you might be using poor technique; make sure you’re shooting at a low ISO and using a fast shutter speed. Mount your camera on a tripod to decrease camera shake even further. When you do handhold, be sure to keep your elbows tucked in tight and your hands steady. Also, make sure your camera is focusing in the right spot.

Second, your lens may simply be blurry at all apertures. This is rare, but it can happen, especially if you’ve purchased a very cheap lens (or you’ve received a bad lens copy). If possible, try a different lens on the same camera. If the issue is instantly resolved, it’s a sign that you should invest in a new lens.

How to find your lens’s sharpest aperture: final words

Now that you know your lens’s sweet spot, you’re ready to capture some tack-sharp shots.

So get out with your camera and start shooting! Be sure to review your results afterward; that way, you can see how much your image sharpness has improved.

Now over to you:

What is your lens’s sweet spot? How did you figure it out? Share your thoughts in the comments below!