How to calculate field of view

Which lens fits the building in, and how far back you need to stand — before you get there.

Field of view is how much of the world a lens takes in on a given sensor. It is the number that tells you whether a shot is possible from where you can actually stand.

Step-by-step

1. Choose your sensor size.
2. Enter the focal length, or the coverage you need.
3. Enter the subject distance.
4. Read the angle of view and the scene width covered.

Focal length alone means nothing

A 50 mm lens is a standard lens on full frame, a short telephoto on APS-C, and distinctly wide on medium format. The focal length is a property of the lens; the field of view is a property of the lens and the sensor together, which is why crop factor exists as a concept.

Working out what you need

The common problem is fitting something in from a fixed position — a building across a street, a group in a small room. Enter the width you must cover and the distance available, and the calculator gives the focal length required. That is a far better way to decide which lens to carry than guessing.

The distinction from perspective

Changing focal length changes how much you include. It does not change perspective — the relationship between near and far objects. That is set purely by where you stand.

So stepping back and zooming in is not equivalent to staying put and zooming out. The first compresses the scene; the second exaggerates depth. This is why portraits shot from close with a wide lens look wrong: the problem is the distance, not the lens.

Frequently asked questions

What is crop factor?

The ratio between a sensor's diagonal and full frame's. It lets you compare fields of view across formats — a 35 mm lens on a 1.5x sensor frames like a 52 mm on full frame.

Does a longer lens compress perspective?

No. Perspective depends only on where you stand. A longer lens is usually used from further away, and it is the distance that produces the compression.

What lens do I need to fit a whole building in?

Enter the width to cover and the distance you can stand back, and the calculator gives the focal length. If the answer is impractically wide, consider a panorama instead.