Focal length and framing: where you stand decides the picture
Focal length is usually explained as how close you can get. That is the least interesting thing it does. What it really decides is where you have to stand, and standing somewhere else changes everything.
Focal length is a decision about distance
One fact does most of the work in this guide: perspective depends only on where the camera is. The relative sizes of a near thing and a far thing are set by the distance from the camera to each of them, and by nothing else. Change the lens without moving and you get a crop of the same perspective. Move, and the perspective changes whatever lens is fitted.
The lens does one thing: it sets how much of the scene lands on the sensor. But because you almost always want the subject to fill a certain part of the frame, choosing a focal length is really choosing how far away you will stand. That is why the same person photographed at 24 mm and at 135 mm looks like two different people, even though the head is the same size in both frames.
What wide, standard and telephoto each do
Wide, roughly 16 to 35 mm
A wide lens makes you stand close, and standing close stretches the distance between near and far. The foreground looms, the background retreats, lines converge hard towards the edges. This is why a wide lens is right for a small room or a landscape with something interesting at your feet, and wrong for a face at arm length: anything nearest the lens, which at that distance is a nose, is rendered larger than it looks in life.
Standard, roughly 40 to 55 mm
A standard lens puts you at roughly conversational distance for a half-length picture and renders relative sizes about as the eye judges them. It is the least dramatic focal length and the most useful one, which is why 18 of the 65 lenses here are classed as standard and why the cheap fast primes at 220-€280 all live in this range.
Telephoto, 85 mm and up
A telephoto makes you stand back, and standing back flattens the difference between near and far. Faces look right. Backgrounds pile up behind the subject, larger and less distinct. A crowd looks denser than it is, and a row of buildings appears stacked. None of this is done by the lens. It is done by your feet.
Compression, and why portraits are shot long
Compression is the most misused word in photography. Long lenses do not compress anything; distance does. What happens is that a long lens forces you back, and from further away the far things and the near things are at more similar distances from the camera, so their relative sizes become more similar.
The arithmetic is worth knowing. Double the focal length and double the distance and the subject stays exactly the same size in the frame. A distant background - a hillside, a row of trees, a city - renders about twice as large as it did, because it was far away to begin with and the extra distance you walked barely changed how far it is. That is the whole effect: the subject held constant, the background magnified.
It explains portraits. For a head-and-shoulders frame on full frame, a 24 mm lens puts you about half a metre from the face, a 50 mm about a metre, an 85 mm about 1.8 m and a 135 mm about 2.8 m. At half a metre the nose is meaningfully closer to the camera than the ears, so it is rendered meaningfully larger. At two metres it is not. That, and not any quality of the glass, is why portraits are usually shot between 85 and 135 mm equivalent.
Why zooming with your feet is only half true
The advice sounds sensible and is half wrong. Walking closer and zooming in do not produce the same picture. Walking changes the perspective; zooming crops it. If you step back to fit more in, the near objects shrink relative to the far ones, and the picture you get is a different picture, not a wider version of the one you had.
So the advice is sound as a discipline and unsound as an equivalence. Using a prime does teach you to see one field of view and to solve framing with your position, which is a genuine skill. It cannot substitute for reach when there is a river, a fence, a stage or a nervous animal between you and the subject - and those situations are most of what a telephoto exists for.
There is honest disagreement about which is the better way to learn. The decision rule is about constraint: if your subject lets you choose where to stand, a prime will teach you more and cost less. If your subject decides the distance, buy the zoom and spend the discipline elsewhere.
Focal lengths that suit common subjects
| Subject | Equivalent | Where it puts you | What it does |
|---|---|---|---|
| Interiors, tight streets, foreground landscape | 16-24 mm | Very close to the nearest thing in frame | Stretches near against far; distorts a face badly |
| A person in their environment, documentary | 28-35 mm | Inside the scene, about an arm and a half away | Keeps context; demands you get close |
| General use, one-lens days, groups, food | 40-55 mm | About where you would stand to talk | Renders roughly as the eye judges it |
| Head-and-shoulders portraits | 85-135 mm | 1.8 to 2.8 m from the face | Natural facial proportions, soft distant background |
| Candid street, sport from the touchline | 135-200 mm | Well back, or behind a barrier | Isolates one subject out of a crowd |
| Birds and distant wildlife | 300-600 mm | As close as the animal will allow | Reach, and a background reduced to colour |
Nothing in that table is a rule. It is a description of where most people end up, and it is a useful starting point precisely because your own figures will differ. Working out what your figures actually are is a half-hour job set out in your first three lenses .
Prepared answers that start from a focal-length need rather than a brand:
The exercise that makes it obvious
Reading about compression does not teach it. Twenty minutes in a park does. You need one zoom, one willing subject or one object about the size of a person, and a background with depth.
Find a subject with a long view behind it
A bench with trees receding behind it, a friend standing in front of a street, a postbox with a row of houses beyond. What matters is that the background is much further away than the subject, because that is where the effect lives.
Shoot it at the wide end
Set the zoom to its widest, walk in until the subject fills about a third of the frame height, and take the frame. Note the focal length and pace out your distance so you can repeat it.
Double the focal length, then double your distance
If the first frame was at 24 mm from two metres, go to 50 mm from four. Adjust your position until the subject occupies the same third of the frame as before. Same aperture, same height, same subject.
Double both again
Now roughly 100 mm from eight metres, subject still the same size. If the lens does not reach, use whatever the longest end gives you and multiply the distance by the same factor.
Compare the three at full size
On a large screen, not on the camera. The subject will be nearly identical in all three. The background will have grown enormously between the first and the last, and the amount of the world visible behind the subject will have collapsed. That is compression, and you produced it by walking.
Repeat it on a face, once
The same three distances on a person shows the other half of the effect: the wide frame exaggerates whatever is nearest the lens, and the long frame does not. Once you have seen it on somebody you know, you will never frame a portrait at 24 mm by accident again.
Do the same exercise at two apertures and you have covered depth of field as well - the details of which are in exposure basics . When you have decided which focal length you keep reaching for, the lens finder will rank the catalogue against it, and if the answer is that you need a different body altogether, start at how to choose a camera . Whatever you end up carrying, camera care and travel covers getting it there intact.
Questions readers ask
- Does a telephoto lens really compress perspective?
- Not by itself. Perspective is set entirely by where the camera stands, and a long lens changes the picture because it makes you stand further back. Shoot a long lens from the same spot as a wide one and you get exactly the same perspective, just cropped tighter.
- What focal length is best for portraits?
- Between about 85 and 135 mm equivalent for head-and-shoulders, because that puts you roughly two to three metres away and the face is rendered with natural proportions. Full-length portraits work fine at 50 mm. Environmental portraits are often shot at 35 mm on purpose, accepting the exaggeration in exchange for context.
- Is a 35 mm or a 50 mm the better single lens?
- It depends on whether you photograph places or people. A 35 mm includes more of the room and suits documentary and travel work; a 50 mm isolates better and suits people and objects. The honest test is the focal-length spread in your own last hundred keepers.
- Do I lose quality by cropping instead of using a longer lens?
- You lose pixels and you keep the perspective of where you stood, which is the more important loss. A crop of a wide frame will never look like a frame shot from further back with a longer lens, because the near-far relationships are baked in at the moment of exposure.