While primarily a planetarium software, Stellarium includes a powerful "Oculars" plugin that offers a highly realistic simulation of your FOV. Field of View Calculator - astronomy.tools
The on Astronomy.tools is built on the Nyquist sampling theorem. In simple terms, to capture a round star, the "point" of light needs to fall on a sufficient number of pixels. If it falls on too few (under-sampling), stars appear blocky. If it falls on too many (over-sampling), you're losing field of view and sensitivity. The calculator uses your local seeing conditions (typically 2-4" FWHM) to determine the optimal pixel scale, which is usually between 0.67" and 2" per pixel for most deep-sky astrophotography.
No accounts, no complicated menus. Enter your scope’s focal length and eyepiece specs. It gives you the TFOV in degrees and arcminutes instantly. astro fov calculator top
For cameras, the FOV is determined by the telescope's focal length and the size of the camera's sensor. Using the sensor's dimensions, you can accurately calculate your field of view: FOV (in degrees) = 2 × arctan(Sensor Size / (2 × Focal Length))
“Aperture shows you what’s there — but FOV shows you where to look.” If it falls on too few (under-sampling), stars appear blocky
Excellent for visualizing the FOV difference between a 1.25" and 2" eyepiece.
Widely considered the for its versatility and ease of use, this tool is often the go-to for astronomers of all skill levels. Its clean interface is divided into three main modes: Visual Mode for eyepiece simulation, Imaging Mode for camera and telescope combinations, and Binoculars Mode for simulating the view through binoculars. You can select your target from a comprehensive list of planets, Messier objects, and nebulae, or search for any object by name or catalog number (e.g., "M31" for the Andromeda Galaxy). If your specific equipment isn't listed, you can create a custom configuration by entering its specifications. No accounts, no complicated menus
Knowing the FOV is crucial in astronomy for several reasons: