FOV & Focal Length: Field of View Explained
Understand the relationship between field of view (FOV) and focal length, how sensor crop affects angle of view, and how equivalent focal length is calculated.
When shopping for phones, you see labels like "13mm ultrawide", "24mm main", "85mm telephoto". What do these focal length numbers mean, and how do they relate to actual angle of view?
Focal Length and Field of View
Focal length is the distance from the lens optical center to the sensor, measured in mm. It determines the field of view (FOV) — how much of the scene the camera captures.
On a full-frame (36×24mm) sensor, the relationship between focal length and diagonal angle of view:
| Focal Length | Diagonal FOV | Common Use |
|---|---|---|
| 13mm | ~118° | Ultrawide / Architecture / Landscape |
| 24mm | ~84° | Main / Everyday / Street |
| 35mm | ~63° | Documentary / Environmental portrait |
| 50mm | ~47° | Standard / Portrait |
| 85mm | ~29° | Mid-telephoto / Portrait |
| 120mm | ~20° | Telephoto / Distance |
| 240mm | ~10° | Super-telephoto / Wildlife |
Equivalent Focal Length
Phone sensors are much smaller than full-frame, so phone focal length labels are typically equivalent focal length — "what full-frame focal length would produce the same angle of view".
Equivalent Focal Length = Physical Focal Length × Crop Factor
Example: physical focal length 8.6mm, crop factor 3.52x, equivalent = 8.6 × 3.52 ≈ 30mm.
Crop Extrapolation
PhoneCameraData charts use crop extrapolation logic:
- A camera has known native image quality at focal length A
- If the sensor is cropped to full-frame focal length B, equivalent aperture scales proportionally
- Cropped equivalent aperture = original equivalent aperture × (B / A)
This is why charts show solid dots (native focal lengths) connected by lines (extrapolated regions).
Multi-Camera Phone Systems
Flagship phones typically use 3-5 cameras covering different focal lengths:
- Ultrawide: 13-16mm, for architecture and landscapes
- Main: 23-24mm, the everyday workhorse
- Mid-tele: 35-50mm, portraits and street photography
- Telephoto: 70-85mm, close-up portraits
- Periscope super-tele: 120mm+, long-distance shooting
Some models (e.g. OPPO Find X8 Ultra) use dual telephoto setups with two different focal lengths to cover a wider mid-to-long range.
Open the "FOV & Focal Length Simulator" in Related Tools to switch sensor sizes and focal lengths and see angle of view changes.