Field of View (FoV) represents the extent of the observable world visible through an optical instrument or sensor. It defines how much of a scene an optical system, such as a camera, telescope, or microscope, can capture. Understanding FoV is fundamental across various fields, from photography to scientific research, as it dictates the scope of what can be perceived or recorded and helps determine appropriate equipment.
What Field of View Means
Field of View describes the angular or linear extent of a scene an optical system can image. It is quantified in two ways: angular FoV, measured in degrees, and linear FoV, measured in units of length at a specific distance. Angular FoV is commonly used for instruments like telescopes and binoculars, indicating the sweep of the scene visible through the eyepiece. Linear FoV applies to cameras and microscopes, describing the physical dimensions of the area captured or observed.
For instance, an astronomer considers angular FoV to determine how much of the night sky a telescope can capture. A photographer focuses on linear FoV to understand the physical width and height of the scene a camera lens will include in an image. This distinction is important across various fields, as FoV directly impacts what can be seen and analyzed.
How to Calculate Field of View
Calculating Field of View involves specific formulas tailored to the optical instrument.
Cameras and Photography
For cameras, linear FoV depends on the lens’s focal length and the camera’s sensor size. The angular FoV formula (which can then be converted to linear FoV at a given distance) is: FoV = 2 arctan(Sensor Size / (2 Focal Length)). Sensor size can refer to the width, height, or diagonal dimension, determining the corresponding horizontal, vertical, or diagonal FoV.
Telescopes and Binoculars
True angular FoV is determined by the eyepiece’s apparent field of view (AFoV) and the system’s magnification. The calculation uses: True FoV = Apparent FoV of Eyepiece / Magnification. Magnification is derived by dividing the telescope’s focal length by the eyepiece’s focal length. For example, a 50-degree AFoV eyepiece with 100x magnification yields a true FoV of 0.5 degrees.
Microscopes
Microscopes use a different approach based on the eyepiece’s field number and the objective lens’s magnification. Linear FoV in millimeters is calculated using: FoV (mm) = Eyepiece Field Number (mm) / Objective Magnification. The field number, typically printed on the eyepiece, represents the diameter of the field of view at the intermediate image plane. For example, a 10x objective with a 22 mm eyepiece field number provides a FoV of 2.2 mm.
Practical Estimation
When precise technical specifications are unavailable, linear FoV can be estimated practically. This involves observing a ruler or a known object placed at a specific distance through the optical system and directly measuring the observable area. This empirical approach provides a real-world measurement of what the system can capture.
What Affects Field of View
Several factors directly influence an optical system’s Field of View, altering the extent of the observable scene.
Focal Length
Focal length, a fundamental property of a lens, plays a significant role. Shorter focal lengths are associated with wider FoVs, capturing more expansive scenes, characteristic of wide-angle lenses. Longer focal lengths result in a narrower FoV, providing a magnified, zoomed-in view, typical of telephoto lenses.
Sensor Size
The size of the image sensor or film format also impacts FoV for a given focal length. Larger sensors capture a wider portion of the scene compared to smaller sensors when paired with the same lens. This means a camera with a larger sensor will inherently have a broader FoV than one with a smaller sensor, even if using an identical lens.
Magnification
Magnification, particularly in instruments like telescopes and microscopes, has an inverse relationship with FoV. As magnification increases, the FoV narrows, allowing for more detailed examination of a smaller area. Decreasing magnification widens the FoV, useful for surveying larger regions.
Working Distance
For microscopy and machine vision, working distance (the distance between the objective lens and the sample) also affects the observable area. Working distance, while not directly determining the lens’s inherent FoV, can influence the effective area in focus or the scale of the image projected onto the sensor.
Using Field of View in Real Life
Understanding Field of View is applied across numerous real-world scenarios, optimizing optical system performance.
Photography
In photography, FoV guides lens selection. Wide-angle lenses with broad FoVs are chosen for landscapes or architecture to encompass vast scenes. Telephoto lenses with narrow FoVs are preferred for portraits or wildlife to isolate subjects.
Astronomy
Astronomers leverage FoV to select appropriate eyepieces for their telescopes. A wide FoV eyepiece is ideal for observing large celestial objects like star clusters or nebulae, providing an expansive view. For detailed observations of planets or the Moon, a narrower FoV eyepiece is chosen to achieve higher magnification and resolve finer details.
Surveillance and Security
In surveillance, FoV is important for camera placement and lens selection to ensure comprehensive area coverage. A wide FoV camera monitors broad spaces like parking lots. A narrow FoV camera focuses on specific entry points, providing clearer identification.
Gaming and Virtual Reality (VR)
Gaming and VR applications utilize FoV settings to enhance immersion. A wider FoV in VR headsets creates a more realistic and encompassing virtual environment, reducing motion sickness and improving spatial awareness.
Microscopy
Microscopy benefits from FoV considerations when examining specimens. Lower magnification objectives offer a wider FoV, allowing scientists to survey an entire sample or locate specific regions of interest. Higher magnification objectives with narrower FoVs are then used to observe intricate cellular structures or microorganisms in greater detail.