Best Lens for Portraits: at 85mm You Have to Step Back 2.43 Times More Than at 35mm

The best lens for portraits isn't fixed: going from 35 to 85 mm means moving back 2.43 times for the same framing, with the field of view dropping from 54.4° to 23.9°.

If you're the one choosing the best lens for portraits, the question that matters isn't which lens is "better": it's how far back you'll have to stand. Moving from 35mm to 85mm to frame the same face means stepping back 2.43 times (1.7 from 50mm). It's an own calculation, on full-frame sensor optics, checked against the cameras behind the 20 photo shoots in the archive: Nikon D810 and D750, both FX, zero APS-C bodies.

And it doesn't measure anything else. The figure doesn't say which lens gives the better result: it says how much working distance and field of view change between 35, 50 and 85mm. The proportions of a face — nose, ear, at each focal length — aren't in this data.

How much does the field of view change between 35, 50 and 85mm?

Horizontal field of view and the distance needed to keep the same framing of a face, using the standard optics formula (field of view = 2·atan(sensor width ÷ (2·focal length))) on a 36×24mm full-frame sensor:

What almost nobody accounts for

Field of view doesn't drop the same amount at each step. From 35 to 50mm it falls 14.8° (54.4° to 39.6°); from 50 to 85mm it falls almost the same, 15.7° (39.6° to 23.9°). The first lens change cuts nearly as much field as the second.

Distance grows in the exact same proportion as focal length. 85 ÷ 35 = 2.43, and the distance for the same framing rises exactly 2.43 times. That's the thin-lens approximation: it holds because at portrait distance (1-3m) the distance is far greater than the focal length.

The archive doesn't support a side-by-side comparison. Only two shoots in the bank have all three focal lengths on the same subject: Pilar & Gustavo and Valeria & Dieter. This is reproducible geometry for any full-frame camera, not a census of which lens gets used most for portraits.

What to do with this when choosing a lens

Choosing a lens means choosing a working distance, not a number stamped on the barrel. If you're going to move to test all three focal lengths on the same framing, it's worth measuring the light first: in the guide to lighting setups in degrees , it's calculated how much a source opens up at different distances, the same kind of geometric calculation as this one.

Frequently asked questions

What's the best lens for portraits, 35, 50 or 85mm?

There's no fixed "best": each focal length asks for a different distance for the same framing of a face. At 85mm you step back 2.43 times more than at 35mm; at 50mm, 1.43 times. It's a choice of working distance, not one focal length beating another.

What's the ideal focal length for a portrait?

There's no single ideal distance: it depends on the space available. At 35mm the horizontal field of view is 54.4°; at 50mm, 39.6°; at 85mm, 23.9°. Less room to move calls for a focal length with a wider field of view.

How far back do you have to step going from 50 to 85mm?

1.7 times, to keep the same framing of a face. That's the exact ratio between the two focal lengths (85 ÷ 50 = 1.7).

Does this calculation hold for any camera?

It holds for full-frame sensors (36×24mm), like the 20 photo shoots in the archive, all shot on a Nikon D810 or D750. On a smaller sensor, the field of view at each focal length is different.