Living with Photography: Don't Be So Shallow

By Norman Chan

Why you shouldn't always shoot photos at the widest aperture your lens can provide.

I'm back to regularly writing this column. No more excuses. I swear it. And all it took to galvanize me back to action was a disagreement on Twitter. Late last week, Alexis Madrigal of The Atlantic (one of my favorite tech writers) tweeted a link to a guide to taking good photos on the relatively cheap. It was written by Stu Maschwitz, a cinematographer and ex-visual effects supervisor at ILM. The guide makes some pretty good recommendations, and I have no doubt that Stu knows what he's talking about. But I disagree with a few of his tips and wanted to give a second opinion, especially since his guide has been well-praised and linked around quite a bit now. It's not that I think he's wrong about any specific point, but that I think beginners should have more context as to what they're doing when following someone's catch-all recommendations.

The purpose of the guide was to get amateur photographers comfortable with the idea of buying a dedicated DSLR camera, and to show that an investment of $1000 will yield much better and more usable (eg. printable) photos than ones taken with a smartphone or cheap point-and-shoot. In that regard it's great, and I agree with the basic gist: buy a used DSLR body for under $500, a 50mm f/1.8 lens for around $100, and shoot a ton of photos so you can learn the hardware. You can also do the same with a good Micro Four Thirds or APS-C sensor mirrorless camera (refurbished Sony NEX-5N would be my recommendation), but you have more affordable-yet-great lens options with a Canon or Nikon DSLR. I also totally agree with shooting in Aperture Priority mode, using manually-set autofocus points (center), and shooting in RAW if possible. You get the most automatic bang for your buck just by switching from JPEG to RAW, and spending some time tweaking in Lightroom. And I want to give Stu a high-five for hammering home the idea that the biggest hurdle to taking good photos is not getting off your butt and actually taking photos. "Actually do this" is the best photography advice I could give, too.

Where we disagree, then, is on the blanket recommendation of how to configure your camera settings when shooting in Aperture Priority mode. Specifically, Stu's tip of shooting with the aperture of your lens wide open. In the context of his recommendations, that's using something like a Nifty Fifty on a Canon Rebel T3i at f/1.8. His rationale for that setting: "Shooting wide-open will result in two things: First, you can shoot in lower light, and even capture fast motion like kids on a carousel. Second, you’ll get that wonderful shallow depth of field that mushes busy backgrounds into pleasing blobs of light." I think both of those reasons are slightly flawed. In the first case, Aperture Priority and Auto-ISO isn't optimal for fast motion--the camera-dictated shutter speeds in Aperture Priority don't take into account a fast-moving scene, and you actually want to shoot in Shutter Priority or manually lower exposure compensation to avoid blur. In the second case, where Stu champions background defocusing--bokeh--I actually am in the camp that believes that it's too easy to overuse bokeh to ruin portrait photography. In fact, I think that shooting with aperture completely wide open on any "fast" prime lens (f/1.8 or wider) should only be used in very specific circumstances.

Here are four reasons why I rarely ever shoot with my 50mm lens wide open.

1. Lenses Aren't Always Sharp when Wide Open

This is an area where people get fooled by specs when shopping for lenses. Two lenses with the same specs, or even adjusted to the same settings (eg. a 50mm f/1.4 set to f/1.8 compared with a 50mm f/1.8) won't yield the same quality image. Factors like the use of aspherical lens elements and the physical size of those elements can affect sharpness at different aperture settings. A general rule is that a lens will produce the sharpest images at the center of the frame, with edge softness and chromatic aberration creeping in as you get closer to the corners of the image. This effect is most pronounced when the lens is fully wide open, to a point where some fast f/1.4 lenses produce overly soft images, but regain sharpness by just stopped down to f/2.0.

And when you're putting your subjects off the center of the frame--for example when shooting with the "Rule of Thirds"--sharpness at the edges of the frame become that much more important.

Image credit: DPreview

The degree to which a lens loses sharpness when its aperture is wide open will vary from lens to lens, and comprehensive reviews from sites like DPreview will test for sharpness across different aperture settings. A notable case of a high-end lens being not very sharp at max aperture is Canon's 50mm f/1.4, which is something that Sigma's more expensive (and larger/heavier) 50mm f/1.4 improves on. It's one of the reasons I picked up the Sigma. In the case of Canon's Nifty Fifty, you can see a dramatic difference in edge sharpness between f/1.4 and f/2.8.

2. High Bokeh Sacrifices Facial Details in Portraits

I'll admit that when first getting my Sigma f/1.4, I wanted to shoot photos with the lens wide open all the time, too. But it didn't take long for me to realize that an aperture of f/1.4 or f/1.8 is actually impractical for getting ideal portraits. The narrow depth of field is just too shallow.

When thinking about depth of field, you can envision an imaginary plane in space that runs parallel to your camera lens. This plane of focus is where your lens and camera will catch subjects at their sharpest and with the most detail--in focus, as it were. You can also easily imagine this plane moving closer and further away from your camera as you adjust focus manually or use autofocus. As you focus on a subject close to you, objects in the background fade into buttery bokeh, and vice versa. But you should also imagine that this plane has its own degree of depth--an expanding and contracting range for keeping objects in focus. And the wider you open your lens aperture, the narrower that plane becomes. At f/1.4, that plane of focus is but a sliver. (It's also why landscape photographers shoot with aperture closed, sometimes as small as f/22.)

For portrait photography, having such a narrow/shallow plane of focus isn't ideal because you lose a ton of important facial detail to bokeh. Here's are two examples below to illustrate, taken of my housemates Evan and Wes. (Click to enlarge details.)

In this first photo of Evan, I've opened my aperture all the way to f/1.4. I've set the camera to Auto-ISO and Aperture Priority as well, even though there's plenty of natural light coming in through the window. Using center-point auto-focus, I've aimed the camera at Evan's eye and then reframed composition. (Side note for portrait photography: your subject's eye is the most important area to get in focus, so aim for that and then frame accordingly.)

The resulting image is pretty good, and has plenty of the hallmarks of a decent portrait at first glance. Evan's eye is in focus, as are other facial features that lie in that shallow plane (the fringes of his hair, bridge of his glasses.) But the rest of his face, including his mount and chin, fade into bokeh. Let's compare this with a photo shot at f/2.8.

This is basically the same photo, but now the plane of focus is much deeper, enough to include the rest of his face. It's still shallow enough so that everything behind his face, like the couch and even Evan's hoodie, gets some nice defocusing, but the important part of the photo isn't lost. The first photo may qualify as more "artsy," but the latter is much more practical and useful as a portrait. Evan is a real person with a real face, not just a "pleasing blob of light."

This next pair of photos shows the same effect, with the first at f/1.4 and latter at f/2.8.

Sigma 50mm at f/1.4
Sigma 50mm at f/2.8

Notice how at f/1.4, only one of Wes' eyes is even in the focal plane. With these three-quarters portraits, shooting at f/1.4 or even f/1.8 means your subject isn't someone's face, it's just a portion of their face.

Take into account that your subjects may be moving targets--like children--or have deep facial features--like dogs--and you can see why narrowing your depth of field is impractical for portrait photography. Plus, as I said before, f/2.5 or f/2.8 is more than wide enough to capture natural light in the golden hour.

3. Shallow DOF Loses Important Scene Elements

This next reason is an extension of the last. With an extremely shallow depth-of-field, the amount that your background subjects blend into bokeh may also be undesirable. If you're shooting a scene with more than one subject, like a child playing with a dog, it's more than likely that those subjects aren't occupying the exact same focal plane. And if you want to capture the interaction between those subjects, you don't want to do it at the expense of one subject or the other. Since I have neither a child nor a dog, let me use these posable figures to illustrate.

Sigma 50mm at f/1.4
Sigma 50mm at f/2.8

Notice that in the first photo, taken wide open at f/1.4, I wanted to keep the Iron Man figure in focus. But by doing so, I not only the distinct silhouette of the encroaching Batman figure, but also the left arm of the Iron Man figure in the extreme foreground. It's a figure stuck between two de-focused blobs of light. In the second photo, shot at f/2.8, both the Batman figure and more of Iron Man are better defined, so you can actually get a sense of what this "scene" is about.

In some cases, even f/2.8 is far too shallow for group photos. The photo below was taken at f/2.8, but Matt on the right and the crying baby on the left are on slightly different planes, so the camera was only able to get one in focus. For group shots taken in natural daylight, I now stop down to f/4.

4. You Don't Want Too Much Light!

There's sound logic in opening your "fast" lens to its widest aperture to allow in the most amount of light in dark scenes. In fact, the reason wide-aperture lenses are known as "fast" lenses is because the increased amount of light hitting the sensor allows the camera to take photos at a faster shutter at normal exposure. But you should consider the opposite side of this benefit. If you're taking photos on a very sunny day with clear skies, and don't have a Neutral Density filter on your lens (not many beginners do), a wide aperture may be too much for your camera to handle.

The brightness, or exposure, of an image is dependent on three primary factors: the aperture of the lens, the camera's shutter speed, and the ISO setting. Brighter images are produced by widening the aperture, slowing the shutter speed, and increasing the ISO setting, and you typically want to find a balance of low ISO (for clearer photos), fast shutter (for capturing action), and wide aperture (more light). On an extremely bright day, your camera may not be able to close the shutter fast enough to compensate for how much light the wide aperture is letting through. Entry-level DSLRs have a max shutter speed of around 1/4000 of a second, which may sound fast, but may actually be too slow to prevent overexposure, even with ISO set to as low as 100. The result is getting an overblown image that you can't correct, even in Lightroom.

My point isn't that you should never shoot a Nifty Fifty at f/1.8, but that from my experience, you get more balanced results when pushing the aperture up to f/2.5 or f/2.8. Bokeh is not the end all be all of image quality, and I think it's a trick that's too easy to misuse and fall back on (why do you think Instagram's fake bokeh setting is so popular?). Photography practice is about finding the right balance of settings to get your desired result, instead of pushing one setting to its technical limit. And of course, always be shooting.