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This free telescope field of view calculator shows the exact imaging field of view your gear will capture, drawn to scale on real survey imagery. Choose a telescope and camera, and the simulator frames the precise patch of sky your sensor sees — so you know whether a target like the Andromeda Galaxy or the North America Nebula will fit before you set up an astrophotography session.
For astrophotography, field of view depends on your focal length and your camera's sensor size:
The calculator runs this math for you and overlays the result on the sky, including any focal reducer or Barlow factor and camera rotation. It also reports effective focal length and f-ratio, image scale in arcseconds per pixel, sensor resolution, and whether your image scale is well sampled for your site's seeing.
A telescope's field of view is the angular size of the patch of sky your camera captures at once, usually measured in degrees or arcminutes. It is not fixed by the telescope alone — it depends on the focal length together with the size of the camera sensor at the focal plane.
FOV = 2 × arctan(sensor dimension ÷ (2 × focal length)), computed separately for the sensor's width and height. A focal reducer shortens the effective focal length for a wider field; a Barlow or extender lengthens it for a narrower field. This calculator does the math and draws the frame to scale on the sky.
Image scale in arcseconds per pixel should match your sky's seeing. A common target is the seeing FWHM divided by about three — roughly 1–2 ″/px for typical seeing. The calculator's sampling gauge shows whether your camera and telescope are undersampled, well sampled, or oversampled for the site seeing you select.
Use a shorter effective focal length — add a focal reducer or use a faster, shorter scope — or use a camera with a larger sensor. Aperture alone does not widen the field of view; it mainly gathers more light and resolves finer detail.
Not necessarily. Field of view is set by focal length and your camera's sensor size, not by aperture. A large, long-focal-length scope can have a narrower field than a small short-focal-length one; bigger aperture mainly gathers more light and resolves finer detail.
At the same focal length, a larger sensor captures a wider field, because FOV = 2 × arctan(sensor dimension ÷ (2 × focal length)). A full-frame sensor frames much more sky than an APS-C or one-inch sensor on the same telescope. Pick your camera above to see the exact framing.