Field of View Calculator
Free Field view Calculator for observation. Enter variables to compute results with formulas and detailed steps. Get results you can export or share.
Formula
FOV = 2 x arctan(Sensor Width / (2 x Focal Length)) | True FOV = AFOV / Magnification
For cameras and sensors, the field of view is calculated using the sensor width and focal length with trigonometry. For visual observation through a telescope eyepiece, the true FOV equals the eyepiece's apparent FOV divided by the magnification (telescope focal length / eyepiece focal length).
Worked Examples
Example 1: Telescope Visual FOV with Eyepiece
Problem: A telescope with 1200mm focal length and 150mm aperture uses a 25mm eyepiece (52-degree AFOV). What is the true field of view?
Solution: Magnification = 1200mm / 25mm = 48x\nTrue FOV = 52° / 48 = 1.083°\nTrue FOV = 1.083 x 60 = 65.0 arcminutes\nExit pupil = 150 / 48 = 3.13mm\nDawes limit = 116 / 150 = 0.77 arcseconds\nMoon diameters across FOV = 1.083 / 0.52 = 2.1
Result: True FOV: 1.083° (65.0') | 48x mag | 3.13mm exit pupil
Example 2: Camera Sensor FOV for Astrophotography
Problem: A camera with a 36mm sensor width is attached to a 600mm focal length telescope. What is the imaging field of view?
Solution: FOV = 2 x arctan(36 / (2 x 600))\nFOV = 2 x arctan(0.03)\nFOV = 2 x 1.718° = 3.436°\nFOV = 3.436 x 60 = 206.2 arcminutes\nMoon diameters = 3.436 / 0.52 = 6.6
Result: Sensor FOV: 3.436° (206.2') | Fits ~6.6 Moon diameters
Frequently Asked Questions
What is field of view in astronomy and how is it measured?
Field of view (FOV) in astronomy refers to the angular extent of the sky visible through a telescope, binoculars, or camera. It is measured in degrees, arcminutes (1/60 of a degree), or arcseconds (1/3600 of a degree). A wider FOV means you can see a larger area of sky at once, which is useful for finding objects and observing large nebulae or star clusters. A narrow FOV provides higher magnification for planetary and lunar observation. For reference, the full Moon spans about 0.52 degrees (31 arcminutes), so a telescope with a 1-degree FOV would show about two Moon diameters across the eyepiece. Field of view depends on the telescope's focal length and the eyepiece or sensor used.
How does focal length affect field of view?
Focal length has an inverse relationship with field of view: longer focal lengths produce narrower fields of view but higher magnification, while shorter focal lengths give wider fields and lower magnification. For a camera sensor, the FOV is calculated as 2 x arctan(sensor width / (2 x focal length)). For a telescope with an eyepiece, magnification equals telescope focal length divided by eyepiece focal length, and the true FOV equals the eyepiece's apparent FOV divided by the magnification. A 2000mm focal length telescope will show about half the sky area compared to a 1000mm telescope with the same eyepiece. This is why deep-sky imagers often prefer shorter focal lengths for wide-field views.
What is the difference between apparent and true field of view?
Apparent field of view (AFOV) is a property of the eyepiece itself, representing the angular diameter of the visible circle when you look through it without a telescope. Common AFOV values range from 40 degrees for older designs to 100 degrees or more for ultra-wide eyepieces. True field of view (TFOV) is what you actually see through the complete telescope-eyepiece system, calculated by dividing the AFOV by the magnification. For example, a 25mm eyepiece with 52-degree AFOV used in a 1000mm focal length telescope gives: magnification = 1000/25 = 40x, TFOV = 52/40 = 1.3 degrees. Higher AFOV eyepieces provide a more immersive viewing experience and make it easier to locate and track objects.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.
Can I use Field of View Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.