If you’re serious about taking better portraits, then one thing you can do is invest in a lens that caters specifically for the subject. People will tell you that a great portrait can be shot on any lens, and that’s true, but certain types of optics just make it easier to be successful.
Most of the time you’ll want a lens that allows a distortion free view of the subject when you’re framing them closely, and one that has a maximum aperture fast enough to blur out any distractions in the background. Here’s how to pick one for your camera. . .
Pick the right focal length
The focal lengths of lenses most often used for portrait photography combine several things. First a minimum of distortion on the subject, and second a magnification that allows you to frame the subject closely while still standing near enough to communicate with them. For this reason, portrait lenses tend to be around 70mm to 135mm in focal length. Anything wider will probably show some distortion when filling the frame with their head and shoulders. Anything longer can mean you’ll probably be too far away to feel connected to them, and may also show distortion, albeit of less unflattering type.
An 85mm or 105mm lens is a great fit for portrait work as they should offer little distortion.
Apply the crop factor
The thing is, that range of focal lengths assumes you’re using a full frame camera– one with a sensor approximately the same size as a frame of 35mm film like a Nikon D850 or Canon EOS 5D Mark IV. When you use a smaller sensor, a crop factor needs to be applied to work out the effect of the lens in traditional terms.
Typically, on cameras with an APS-C sized sensor, like a Canon EOS 80D, Nikon D7200 or Fujifilm X-E3, the crop factor is around 1. 5x, or 1. 6x on the Canon. And on Micro Four Thirds cameras like the Panasonic GX9 or Olympus OM-D E-M1 Mark II, it’s 2x.
So, while a 45mm lens on a full frame camera would generally be considered a bit too wide for head-and-shoulders shots, on camera with a 2x crop factor that will be 90mm, and spot on for portraits. Similarly, you can use 50mm lenses on APS-C cameras as they’ll give results similar to a 75mm or 80mm lens.
©Matty Graham
A 45mm lens on a Micro Four Thirds camera gives an effective 90mm focal length, great for portraits. . .
. . . while the a 17-50mm zoom on an APS-C sized sensor will give an effective focal length of 75mm to 80mm.
Pick a maximum aperture
Another characteristic of good portrait lenses tends to be a wide maximum aperture. This is the greatest f/number that’s available on the lens, and an indication of the maximum amount of light it will let in, as well as how shallow a depth-of-field it’s capable of creating.
Typically, good portrait lenses will have low f/numbers like f/2, f/1. 8, f/1. 4 or even f/1. 2, as this lets the photographer keep either only the subject in focus and blur the background, or even keep only the subject’s eyes in focus.
Traditionally the main benefit of a fast aperture, however, is to create a bright exposure, which means shutter speeds can be faster (and therefore the ISO kept lower). For portraits, this is a huge benefit, too, as you’ll be working handheld, and don’t want to blur the subject through camera shake, which can happen at slower shutter speeds.
©Kingsley Singleton
Get a lens with an f/1. 4 maximum aperture and you can create bokeh-filled backdrops.
Zoom or prime?
This combination of short to medium telephoto focal lengths and fast apertures is mostly found in prime lens. It’s simply easier to build such lenses this way, and zoom lenses with fast apertures tend to be bigger and heavier. There are exceptions, though, like Sigma’s 50-100mm F1. 8 DC HSM Art, and a zoom lens will give you more freedom in composition.
Zoom lenses with a constant maximum aperture of f/2. 8 are still fast enough for portraits, so can be a great partner, too. In practice, that could mean using the long end of a standard zoom like a Tamron SP AF 17-50mm F/2. 8 XR Di II VC LD on a cropped sensor, or a Nikon AF-S 24-70mm f/2. 8E ED VR on a full frame camera.
Better still, use a telephoto zoom like a Fujifilm’s XF50-140mm F2. 8 R LM OIS WR, Canon’s 70-200mm f/2. 8L IS II USM, or Sony’s FE 70-200mm f2. 8 G Master, where you can set it to the traditional portrait focal lengths, or use the compressed view of the longer focal lengths that will make depth-of-field seem even shallower.
A fast 24-70mm f/2. 8 zoom can give great portrait results, though you'll want to use it at the long end.
Autofocus performance
AF for portraits needs to be fast and accurate, and preferably quiet. Speed and accuracy aren’t needed because you’re chasing the subject about, but because you’ll probably be shooting at a wide aperture and can’t afford the point of focus to slip without losing sharpness where it’s needed – on the eyes. At very wide apertures and focusing close to the subject, the zone of sharp focus could be less than 1cm. And if you’re using smart AF functions like face- or eye-detection AF, lens performance is just as important, as lenses with slow AF will just slow down the performance of the camera.
©Matty Graham
As well as your handling, fast and accurate AF is vital when working at a very shallow depth-of-field.
Image stabilisation
Many portrait lenses don’t come with image stabilisation – IS, VR, OIS and so on, depending on the make. The reasoning for this is that, as they’re fast lenses and let in a lot of light, you’ll probably have a fast enough shutter speed to avoid camera shake anyway. But a little bit of help doesn’t hurt, and even if your base exposure is a decent 1/125sec and the image is acceptable, a few stops of IS will make it much crisper. Obviously if you’re using a camera with in-body stabilisation you can enjoy its benefit with any lens, but even then manufacturers are adding optical stabilisation to lenses to add even more security.
Not only fast, Tamron's SP 85mm f/1. 8 adds image stabilisation.
. digitalrev.com2018-11-15 03:00
