When we look at the gears of well known portrait photographers in the community, why do we see they use lenses with long focal lengths? Why is it that 85mm focal length is often considered ideal for portraits? What’s wrong with taking portraits with a 24mm f/1.2?
I am going to share whatever insights I have on this topic in this blog post.
Common Expectations
I usually focus on these things while shooting portraits –
- Background Isolation / Background Blur
- Background Compression
- Field of view / Filling the frame
- Minimal distortion on the subject
Background Blur
We want our subject to stand out. And often we like to blur the background behind to isolate the subject in front. This should put the attention on him / her. The amount of blur often depends on what kind of shots we want. Because sometimes a background can add value to the portrait and in such cases, we do not want to blur it out fully. For example, if the subject is wearing a red dress and the background is beautifully green, we can creatively use the background to add contrast to the scene.
Background Blur usually depends on the size of the entrance pupil of a lens. This is usually denoted by f-stop. For the same lens, lower f-number would mean more blur. f/1.2 should have more blur than f/2.8. But the f-stop is a relative number to the focal length. f/2 means the diameter of the entrance pupil is half of the focal length. As you can calculate – f/2 would have different size for a 50mm lens and a 80mm lens. 80mm f/2 would be 40mm while the 50mm f/2 would be 25mm. As a result the longer focal length is expected to provide blurrier background. So yes, a longer focal length lens with higher f-number can sometimes produce more blur than a smaller focal length lens with lower f-number.
But the entrance pupil / aperture / focal length calculation is just one of the factors affecting background blur. The distance between the camera and subject and the distance between subject and background also influences the blur. When we take photos with a short focal length, we can get quite close to the subject. When we shoot with a longer focal length, we usually shoot from afar. This affects the distances mentioned above. But in the end, usually longer focal lengths can produce more blur.
I have a detailed blog post discussing these in depth with simulated illustrations. Please check out Creating Background Blur. In general, longer focal lengths – if used properly can get us more background blur.
Background Compression
Background compression is a kind of distortion where the background gets magnified and squeezed together. If we have a very busy background that doesn’t add much value to our photo, having the background compressed often separates the subject better.
To illustrate this, I have another dedicated blog post on this subject – Background Compression. Please check this out to better understand the concept of background compression.
While using a longer focal length, the background gets compressed more.
Field of View / Filling the Frame
In the first two sections – for both background blur and background compression, I tend to prefer lenses with longer focal lengths. But longer focal lengths also have tighter field of view. The frame would often get filled with your subject. And that too with half the body being in frame. With a longer focal length, I would have to take a few steps back to keep the subject full in my frame.
But what if I also want to include some of the background in the photo? We can use shorter focal lengths for this kind of photos. If we want to fill in the frame with our subject, a longer focal lengths would work better.
I personally would love to take some wide angle portraits when the background contains some beautiful landscape or a contrasting scene.
Distortion
If we put something close to our camera, it would look larger than it actually is. This is more visible in shorter focal lengths aka wide angle lenses. In wide angle lenses, we tend to get quite close to the subject and thus things may look disproportionate. Lines in background don’t look straight. Faces look weird.
If you’re taking portraits with a wide angle lens from up close, you may find that the face or part of the face (say nose) is larger than the other parts of the body. On the other hand if we get too far and start to zoom in on the subject using telephoto lens, faces may start looking larger / wider than their real life size.
Because of these distortions, photographers want to avoid too short or too long focal lengths to avoid distorting the subject or the background.
50mm / 85mm / 135mm
50mm is a pretty standard focal length. It’s very close to the focal length of our eyes. So photos taken at this focal length can look natural. This is also not bad for taking portrait photos. You can take full body portraits or the upper half easily with this focal length. You can even bring in some background with ease.
85mm is often considered an ideal length for portrait photography because you get nice background compression, your subject has a flattering look and you can use background blur to separate the subject better from the background.
135mm should produce photos which seem more flattering than the 85mm. But there’s one downside – we have to step back quite a bit to keep our subject in frame. Which I personally wouldn’t feel very comfortable with.