In photography, we strive to take “sharp” photos. Generally, this means that you want the subject to be in focus with clear lines, crisp details, and no (unintended) blurring. It’s a combination of accurate focus, a static camera, and the properties of the lens you’re using.
One thing to note is that there are two kinds of sharpness: there’s an official optical measure (it’s called acutance) that gets all kinds of complicated fast, and there’s perceived sharpness, which is what photographers mostly want. We’re tackling the latter one today, although there is some overlap with optical sharpness.
So, let’s dig in.
What is Sharpness Anyway?
As defined above, a sharp image is one where the subject of the image—or the bits of the subject you want—are in perfect focus with every detail crisp and clean. Below, is one of my favorite examples of this.
The main “subject” of the photo is Kat’s eyes; they’re so sharp you can see the individual eyelashes even though the focus fades off across her face. Just compare the sharpness of her eyes to the slight blur of her ears and the indistinct background. I know I’m tooting my own horn, but it’s a pretty great example of the classic “portrait look.”
Let’s look at another example, this time from landscapes.
Here the image is sharp throughout the frame, from the rocks in the foreground to the lighthouse in the background. The motion blur in the rocks is just an element of long exposure photography.
In both examples above, the sharpness is a result of accurate focus, a static camera, and the lens and its settings. Let’s take them one by one.
Accurate focus is arguably the most important factor in taking sharp images. If you miss focus, even by a small amount, something will look off with your image and no amount of work in post will save it. I love the photo below of an old man setting up his fishing gear, but I missed the focus.
Even though I was only off by a little bit—somewhere between his hands and his sweater is where the focus rests—the photo is now pretty much unusable for anything but teaching people not to miss focus.
Compare the image to the photo of Kat above. A lot more of that image is blurry but because her eyes are sharp the image works. Here, although the rest of the subject is pretty much in focus, the fisherman’s face isn’t, and the photo doesn’t work.
A Static Camera
For a sharp image, there can be no camera movement in the image. This means one of two things: either you shoot with a fast enough shutter speed to freeze motion or you use a tripod to lock your camera down.
Which option you use depends on what sort of photograph you’re trying to take. For a portrait, you’ll need to use a fast shutter speed. For a landscape, you can either go with a fast shutter speed or a tripod if you want to use a longer exposure time.
The Properties of the Lens You’re Using
Lenses are far more important than your camera when it comes to image quality. Even the most basic of DSLRs can take great, sharp photos while a bad lens will render ten grand worth of camera worthless.
In general, good lenses—which means expensive lenses—deliver greater sharpness throughout the image, referred to by photographers as “edge-to-edge sharpness.” Cheaper lenses will probably take images where the center of the image is sharp, but the edges are blurry.
Better lenses also have less optical distortion or chromatic aberration. You can see a small loss of edge sharpness in the image below of a newspaper. The block of text on the left is from the center of the image while the block on the right is from the edge. I used a Canon 50mm f/1.8 for this test.
Lenses don’t have the same quality throughout their whole range, which can make matters even more confusing. Most lenses have a “sweet spot” aperture where they’re at their sharpest. It’s normally at some point between f/5.6 and f/16 depending on how the lens is designed.
To get an idea of how sharp the lenses you shoot with are and when they’re at their best, check out the reviews on DxOMark.
So there you have it: sharpness is focus plus a decent lens—so long as you don’t fumble your camera while taking the shot.