A 90-degree Field of View (FOV) corresponds to an 18mm focal length when using a full-frame camera sensor. This relationship is fundamental in photography, determining how much of a scene a lens can capture.
Understanding Field of View and Focal Length
- Field of View (FOV): Refers to the extent of the observable world seen at any given moment through a camera lens. It's typically measured in degrees. A wider FOV means you see more of the scene, while a narrower FOV shows less.
- Focal Length: This is a property of the lens, measured in millimeters (mm), representing the distance from the optical center of the lens to the camera's sensor when the subject is in focus at infinity. Shorter focal lengths (e.g., 18mm, 24mm) result in a wider FOV, while longer focal lengths (e.g., 200mm, 300mm) produce a narrower FOV, magnifying distant subjects.
Focal Lengths and Corresponding Fields of View
The relationship between focal length and FOV is crucial for photographers to select the right lens for their desired perspective. The table below illustrates how different focal lengths affect the field of view, particularly for a full-frame sensor, where a 90-degree horizontal FOV is achieved with an 18mm lens.
| Focal Length | FOV (Horizontal in degrees) | FOV (Vertical/Diagonal in degrees) |
|---|---|---|
| 18mm | 90.0 | 66.0 |
| 19mm | 86.9 | 63.2 |
| 20mm | 84.0 | 60.7 |
| 24mm | 73.7 | 52.0 |
Note: The second FOV column (e.g., 66.0 for 18mm) can represent either the vertical or diagonal field of view, depending on the specific measurement standard used.
The Influence of Sensor Size on FOV
It's important to recognize that the FOV produced by a specific focal length is also significantly influenced by the size of the camera's sensor. The values in the table above are typically associated with a full-frame sensor (36mm x 24mm), which is considered the standard reference.
- Full-Frame Sensors: Provide the widest FOV for a given focal length.
- Crop Sensors (e.g., APS-C): Smaller sensors result in a narrower FOV compared to a full-frame sensor for the same focal length. This is often referred to as a "crop factor." For instance, an 18mm lens on an APS-C sensor (with a 1.5x or 1.6x crop factor) would have an equivalent FOV closer to a 27mm or 28.8mm lens on a full-frame camera.
Practical Applications
Understanding FOV and focal length is essential for:
- Composition: A wider FOV (shorter focal length) is ideal for capturing expansive landscapes, architectural interiors, or large groups of people. A narrower FOV (longer focal length) is suited for isolating subjects, portraits, or wildlife photography.
- Lens Selection: Photographers choose lenses based on the desired perspective and how much of the scene they want to include. For example:
- To achieve a wide, immersive perspective similar to a 90-degree FOV, an 18mm lens on a full-frame camera is a go-to choice.
- For closer perspectives or more compressed backgrounds, longer focal lengths are preferred.
- Videography: FOV also dictates the "look" of video footage, from wide establishing shots to tight close-ups.
For more detailed FOV tables and comparisons across various focal lengths and sensor sizes, you can refer to resources such as FOV Tables: Field-of-view of lenses by focal length.
