10. CHOOSING A LENS AND FOCAL LENGTH
THE KIT LENS that came with your camera or a standard zoom lens is really all you need for great portraiture. I know plenty of professionals that shoot portraits with a kit zoom lens, and I’m quick to grab my 24-70mm for the same reason. However, the search for the perfect portrait lens and focal length is a highly subjective journey. Some folks enjoy using lenses with only one focal length (called a prime lens), and some folks want nothing more than a very fast lens (a lens capable of opening its aperture as much as possible).
To find the portrait lens that works best for you, it helps to know a few key characteristics of lenses and focal lengths. These characteristics include a lens’s maximum aperture opening, the quality grade of the glass, and its build quality. The most important characteristic to consider, however, is lens perspective.
Perspective refers to the size of the subject as it appears in the frame and the spatial relationship objects have to each other. All lenses are identified by the focal lengths they provide. Wide-angle focal lengths range from 8mm to somewhere around 35mm; standard zoom focal lengths range from 24mm to 70mm; and telephoto focal lengths go beyond 70mm. Lens focal lengths exist on a limited range, from ultra-wide to super-telephoto. However, it’s most important for us to correlate focal lengths to the perspective they visually convey. The shorter the focal length (the more wide-angle the lens), the more expansive the image’s perspective will be. This means that subject matter in the foreground will appear much larger compared to all other subject matter, and the distance between the foreground and background will appear more extensive (Figure 10.1). Inversely, as the focal length increases (telephoto lens), the perspective changes to reveal a more compressed image. This compression perspective closes the distance between the foreground and background, which makes the background seem more spacious (Figure 10.2). Normal perspective falls in between expansive and compressed perspectives. Normal perspective visually conveys the same perspective of our own eyes, displaying subject matter in proportionate relationship to each other as we see them outside the viewfinder. Normal perspective is typically associated with 50mm (thus explaining the popularity of such prime lenses) (Figure 10.3). Although the numbers next to the abbreviation for millimeters might be an impressive talking point at the local camera club, it is the correlation between those numbers and perspective that will inform your creative decisions regarding making great portraits.
10.1 Using a super-wide-angle focal length expands the distance between the car headlights closest to camera left and the actual portrait subject. The size of the headlights compared to everything else in the frame is overly exaggerated as well.
ISO 200; 1/160 sec.; f/16; 17mm
10.2 A longer focal length was helpful in pulling all of the vehicles together, or compressing the visual distance between them, creating a layered portrait of the car owner.
ISO 200; 1/80 sec.; f/22; 105mm
10.3 A 50mm perspective most accurately conveys the way our eyes see the world around us, and it is an extremely useful lens when you want to avoid distorting anything in the frame.
ISO 100; 1/1600 sec.; f/2; 50mm
Secondary to perspective, it’s also worth noting that the shorter the focal length is, the more depth of field the image frame gains. The longer the focal length is, the smaller the depth of field will be. For example, a 32mm lens set to f/4 will yield more depth of field (Figure 10.4) than a 105mm lens set to f/4, which will yield little depth of field (Figure 10.5). Some argue that there is no difference, but you can’t argue with how the images look. This information may come in handy when you are looking to either include more environment in your portrait, or if you want to isolate the subject against a soft, out-of-focus background.
10.4 Expansive perspectives often make an image look as though there is more depth of field than the aperture (f/4 in this case) could provide.
ISO 100; 1/50 sec.; f/4; 32mm
10.5 The more you zoom in on an image, the more the visible depth of field decreases, as long as you maintain the focal point on the subject.
ISO 100; 1/50 sec.; f/4; 105mm
Although great portraits are made at all focal lengths, it’s good to start out using a standard to medium-telephoto focal length that offers a slightly compressed perspective. A great favorite amongst portrait photographers is the 85mm focal length. It is longer than 50mm and compresses the portrait subject a bit with the background; yet, it does not distort features like a wide-angle focal length would. The 85mm prime lens is practically made for portraiture. No matter the manufacturer, 85mm primes are fast lenses (the maximum aperture is very large) that open up to f/1.8 (some even open up to f/1.2). This translates into an increased ability to knock the background out of focus, directing full attention to the subject in your portrait (Figure 10.6).
If you don’t want to purchase an 85mm lens, or you need the flexibility of a zoom lens, a standard zoom lens that ranges from 24-70mm will work nicely when zoomed all the way out (or at least past 50mm). Zoom lenses do not have such large maximum apertures, but they provide slight perspective compression and don’t distort the image, so they are great alternatives to the 85mm. Personally, I find myself using a 24-70mm lens that opens to f/2.8 much more than the 85mm f/1.8 I also carry in my bag (Figure 10.7).
10.6 An 85mm prime lens does not distort the frame or the subject, and the slightly compressed perspective helps create great backdrops for portraits, especially when the aperture is wide open and the depth of field is decreased considerably.
ISO 200; 1/400 sec.; f/2.2; 85mm
10.7 A 24-70mm lens is often my go-to for portraits when I’m doing editorial work because of the flexible range of accessible focal lengths. This portrait of a barge worker benefitted from the longer end of the standard zoom lens.
ISO 100; 1/2000 sec.; f/2.8; 70mm
10.8 I shot this portrait at 75mm on a camera with a full-frame sensor. The red line represents the size of the frame using the same lens on an APS-C sensor with a 1.5x crop factor, equating to a 112.5mm perspective. Suffice it to say, I would have to back up to keep from cropping out too much of the subject.
Sensor Size’s Effect on Focal Length and Perspective
One of the most confusing things about digital photography is identifying the difference in DSLR sensor sizes and how they affect your image. Although all DSLR sensors and many mirrorless camera sensors share the same 2:3 length-to-width dimensional ratio, not all of them are the exact same size. Most entry-level cameras have a slightly smaller sensor than their higher-end family members. We refer to these as cropped sensors, while calling their larger brethren full-frame sensors. A full-frame sensor is the same size as a frame of 35mm film. Cropped sensors (referred to as APS-C sensors) are smaller, and their size is associated with their crop factor. For example, a Nikon APS-C sensor has a crop factor of 1.5x. A Canon APS-C sensor, on the other hand, has a crop factor of 1.6x. The larger the crop factor (Canon’s, in this case, is slightly larger), the smaller the sensor (Figure 10.8).
So, what does this mean for your portrait making? Full-frame sensors treat the focal length you are using as just that—the focal length you are using. When shooting with a 50mm lens on a full-frame camera, you will be shooting at a true 50mm perspective. That same 50mm lens on an APS-C camera body will visually display a different perspective. Although many folks like to say that an APS-C sensor’s crop factor multiplies the focal length you are using, I like to think about its effect on the perspective with which I’m shooting. You see, if you are using that 50mm lens on an APS-C sensor with a 1.5x crop factor, you are actually seeing (and shooting) with the perspective of a 75mm lens on a full-frame sensor. Many folks purchase 18-55mm kit lenses with their APS-C camera bodies. In full-frame numbers, this lens translates into a 27-82.5mm lens. If you are using a camera with a cropped sensor in it, simply find out the crop factor and multiply it by the focal length you are shooting with in order to determine the actual perspective you are producing in your images.
Remember that 85mm lens I made out to be the best thing since sliced bread? On a cropped sensor with a 1.5x crop factor, its perspective equates to that of a 127.5mm focal length on a full-frame sensor. This isn’t necessarily a problem; it’s simply something to be aware of. Just so you know, if you do want to achieve something close to an 85mm perspective using an APS-C sensor, you’ll want to use a focal length slightly over 56mm.