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Matching lenses from each maker's lineup, plus some classic medium and large format lenses. Email me if something is wrong or missing.
Lens compression
Compression comes from camera distance. A longer lens only makes you stand farther back for the same framing.
Same face, different distance
This page opens a 24mm and a 135mm lens on full frame, both at f/2.8 and both framing the face at the same size. The 24mm camera stands 40 cm from the person, the 135mm camera 2.2 m. From close in, the nose looks larger and the wall seems far behind the person. From farther back, the face looks flatter and the wall looks larger and closer. That is lens compression.
Six focal lengths at the same framing
| Focal length | Camera distance | Horizontal angle of view | Sharp zone at f/2.8 | Blur, wall 2 m behind | Blur, distant background |
|---|---|---|---|---|---|
| 24mm | 40 cm | 74° | 6.4 cm | 1.3% | 1.5% |
| 35mm | 57 cm | 54° | 6.2 cm | 1.8% | 2.3% |
| 50mm | 80 cm | 40° | 6.1 cm | 2.3% | 3.3% |
| 85mm | 1.4 m | 24° | 6.1 cm | 3.3% | 5.6% |
| 135mm | 2.2 m | 15° | 6.0 cm | 4.3% | 8.9% |
| 200mm | 3.2 m | 10° | 6.0 cm | 5.1% | 13.2% |
Full frame, face framing as in the simulator, f/2.8. The sharp zone uses the same circle of confusion as the side view. Blur is the diameter of a blurred point of light as a share of the image width, calculated with the thin-lens formula. In the simulator the wall stands about 2 m behind the person.
What the numbers show
The camera distance grows in step with the focal length. The sharp zone around the face hardly changes: about 6 cm at f/2.8 for every lens, because the framing is the same. Background blur changes a lot. A distant background is about 9 times as blurred at 200mm as at 24mm, because the longer lens has a wider aperture opening at the same f-number. For the wall 2 m behind the person the gap shrinks to about 4 times, because the long lens also stands farther from it.
What to try
Switch to a wider framing: the distances grow, but the comparison holds. Put both lenses on the same f-number, then use Match depth of field to see how far the 135mm has to stop down to blur the background as little as the 24mm. For pairs closer together, open a lens comparison such as 35mm vs 85mm or 85mm vs 135mm.
Questions
What is lens compression?
The look of a background that seems larger and closer to the subject in a telephoto picture. It comes from standing farther away. The longer focal length is what keeps the subject the same size from that distance.
Does focal length change perspective?
Not by itself. From the same spot, a 24mm picture cropped to the framing of a 135mm picture has the same perspective. Perspective changes when the camera moves, and for the same framing a longer lens needs the camera farther back.
Which focal length is best for a head-and-shoulders portrait?
There is no single answer. On full frame, 85mm to 135mm keeps the camera about 1.4 m to 2.2 m from the face in the simulator's face framing, far enough that features keep their proportions. 35mm and 50mm show more of the place and bring you closer, which enlarges whatever is nearest to the lens.