Understanding the creative aspect of lens aperture

We all learn in Photography 101 that the aperture setting is a physical property of the lens, and you can vary its size to control the amount of light entering your camera. Usually, we think of aperture as it relates to the rules of exposure.

Back when I was shooting film and early digital cameras, it was considered ideal to have a “fast” lens (meaning one with an aperture of f/2.8 or wider). Why? because with limited ISO options (remember film rarely was faster than ISO 800 and early DSLRs got noisy in a hurry above ISO 400), a fast lens meant you could shoot hand-held in dim conditions without a flash.

Today, ISO no longer limits most photographers. Sure, images are still cleaner and have greater dynamic range at a camera’s base ISO, but you can shoot above ISO 6400 these days pretty much with impunity. That means you have much more creative latitude to choose the aesthetic of your shots by varying the lens aperture.

Depth of field as a creative tool

If you ask a non-photographer what makes a shot look “professional,” they might not know the right answer but it almost always comes down to depth of field. Smartphone cameras and most point and shoot cameras have sensors that are so small that everything is sharp from foreground to background. That kind of look is fine for landscapes (Ansel Adams was a member of the f/64 club, after all), but isolated subjects with smooth, out of focus backgrounds create a unique look in photographs. It’s why smartphone makers have started implementing computational photography tools like “Portrait Mode” in their camera software, and why many photographers gravitate towards Aperture-priority exposure mode.

If you’re using a standard digital camera, depth of field comes down to these four parameters:

• Lens aperture (f-stop)
• Subject distance (focus distance)
• Lens focal length
• Sensor size

In a nutshell, you’ll get more subject isolation (and a softer background) from a fast telephoto lens focused fairly close to the subject. As you stop down, go wider, or focus farther away, depth of field increases. Cameras with small sensors will produce images with greater apparent depth of field than those with large sensors when the images are framed identically and shot at the same aperture setting.

The good and bad of shallow depth of field

Depending on your style of photography, shallow depth of field (DoF) can be your friend or your nemesis. For example, portrait photographers love shallow DOF images, and often invest in lenses that deliver that look, like an 85mm f/1.2 or a 105mm f/1.4. On 35mm format cameras, you’ll get razor thin DoF and great subject isolation. It also makes focusing extremely critical, because at these settings, the focal plane is incredibly thin.

On the other hand, there are plenty of situations where more DoF is required or actually preferred. Landscape photographers often shoot stopped down to f/11 or more to get everything sharp from foreground to background. Macro photography is a particular challenge, because at extreme close focus distances, DoF is practically nil, even at f/32.

Light plays a part, too

It’s important to keep in mind that as you change lens aperture settings, your exposure settings will change, too. Stopping down is going to require either slower shutter speeds, increased ISO, or the use of a flash. Shooting wide-open in bright light can present challenges, too. If your camera doesn’t offer very fast shutter speeds or doesn’t have extended low ISO settings, your images could end up overexposed.

Choose the gear that’s right for you

When choosing a camera, keep in mind what your primary subjects tend to be. All of today’s modern mirrorless cameras are excellent in terms of image quality, so look at the lens lineup and consider sensor size. If super thin DoF is your goal, you’ll likely want to use a 35mm format camera with fast glass (f/2.8 or faster). Those cameras and lenses tend to be larger, heavier, and more expensive than those with smaller sensors.

If, on the other hand, you are interested in landscape or macro photography, then maybe fast lenses aren’t necessary. There are many outstanding lenses with f/4 maximum apertures that are smaller, lighter, and less expensive than those f/1.8 models. On a micro 4/3 system body, the apparent DoF (how it appears) is 2x that of a 35mm format camera. That means you can shoot wide-open with an f/4 lens and have the look of shooting 35mm at f/8. That is a tremendous advantage if you’re shooting landscapes or closeups, because you’ll have 2 stops more light to play with compared to a 35mm format camera.

Getting shallow depth of field using post-processing

What if you don’t have a super fast lens, or you prefer the smaller form factor of an APS-C or Micro 4/3 format camera? There are still some tricks you can do to soften the backgrounds of your images and take some of the edge off. These techniques can also be helpful if your particular lens doesn’t produce pleasant out of focus rendering (bokeh).

Adobe Lightroom: Negative Texture

If you use Adobe Lightroom / Lightroom Classic or Adobe Camera Raw, there’s an easy way to soften your backgrounds just enough to improve subject isolation. Select the background using Lightroom’s Masking Panel, and then dial down the Texture slider. It’s quick, easy, and works quite well most of the time. You can also experiment with using negative Clarity and negative Sharpening settings to get the look you want.

Adobe Photoshop: Depth Blur Filter

Adobe Photoshop users can experiment with a new filter called Depth Blur to create the appearance of shallow depth of field. In Photoshop, you’ll find Depth Blur under Filters–> Neural Filters. Choose the Depth Blur option and you’ll be given tools to set the focus area, adjust the blur amount, and set the depth. Depth Blur is an AI-based filter and requires some serious GPU horsepower to run. If you’re on an older computer, you might be waiting a long time for the effect to process.

In conclusion, lens aperture plays an extremely important role in photography. It not only affects your exposure settings, but it also helps define the aesthetic in your photos. By understanding ways to control depth of field, both in-camera and in post-processing, you’ll be able to make images that suit your creative vision and style.