Lesson 3 of 4

Distance and background

Keep the car the same size in the frame and change the lens. The car does not move. Everything behind it does.

There is no distance slider on this page, and that is the lesson. Once you decide how big the car should be in the frame, the focal length decides where you have to stand. You do not get to pick both.

The fence behind the car has a post every two metres. The car is drawn at the same size in every configuration, because the distance is recalculated to keep it there. Move the focal length and count the posts.

24 millimetre lens on a Full frame sensor. To fill 80 percent of the frame with a 4.5 metre car you stand 3.8 metres away, which shows 65.6 metres of background, about 33 fence posts.THE FRAME — SUBJECT SIZE HELD CONSTANT65.6 m OF BACKGROUND ACROSSLENS3.8 m43.8 m

The fence behind the car has a post every two metres. The car is drawn at the same size in every configuration, because the distance is recalculated to keep it there. Count the posts as you move the focal length.

FULL SUBJECT33 fence posts behind the car
24 mm — stand 3.8 m back
Short lens up close: the near end of the car looms and the far end shrinks awayLong lens from far back: the same car size, with the background stacked flat behind it
Ultra wideLong telephoto
40 m behind
Against the carFar off
80% of the frame width
Small in frameEdge to edge

A smaller sensor needs a shorter lens for the same framing, so it puts you closer, so it takes more background with it.

Stand back
3.8 m
Background across frame
65.6 m
Background sweep
11.67 frame widths
Near / far size ratio
1.67 : 1

Presets

Compression is a distance effect

A long lens is often described as compressing perspective. It does not. Hold the subject size constant and the required distance is proportional to the focal length, so doubling the lens roughly doubles how far back you stand. From twice as far away, the ratio between the distance to the car and the distance to the fence behind it drops, and the fence renders larger relative to the car. Crop a wide-angle frame down to the same subject size and you get the same relationship between car and background, just with fewer pixels. The lens changed nothing except where your feet had to be.

What this buys you

A short lens at close range sweeps a wide arc of whatever is behind the subject into the frame: the other cars, the fence, the building, the sky. A long lens from far back picks out a few metres of it. If the location is good, take the wide one. If the location is a car park, the long lens is how you make most of it disappear without moving the car.

Sensor size does the same thing

Switch to the phone sensor and watch the distance readout collapse. A small sensor needs a short lens for the same framing, and a short lens puts you close, and close is where the background sweep is widest. That is why a phone photograph of a car tends to arrive with the whole street attached, and why stepping back and using the phone's longer camera changes the picture more than any edit will.